diff --git a/src/ast/ast_common.hpp b/src/ast/ast_common.hpp
index 96fd6a7f7d..a167cd9624 100644
--- a/src/ast/ast_common.hpp
+++ b/src/ast/ast_common.hpp
@@ -23,10 +23,8 @@
 #include "symtab/symbol_table.hpp"
 #include "visitors/visitor.hpp"
 
-namespace nmodl {
-
 /// Abstract Syntax Tree (AST) related implementations
-namespace ast {
+namespace nmodl::ast {
 
 /**
  * @defgroup ast AST Implementation
@@ -96,5 +94,4 @@ static const std::string ReactionOpNames[] = {"<->", "<<", "->"};
 
 /** @} */  // end of ast_prop
 
-}  // namespace ast
-}  // namespace nmodl
+}  // namespace nmodl::ast
diff --git a/src/codegen/codegen_acc_visitor.cpp b/src/codegen/codegen_acc_visitor.cpp
index 03a7589ff7..05e1fd6f92 100644
--- a/src/codegen/codegen_acc_visitor.cpp
+++ b/src/codegen/codegen_acc_visitor.cpp
@@ -12,8 +12,7 @@
 #include "ast/protect_statement.hpp"
 
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 /****************************************************************************************/
 /*                      Routines must be overloaded in backend                          */
@@ -376,5 +375,4 @@ void CodegenAccVisitor::print_dt_update_to_device() const {
                       get_variable_name(naming::NTHREAD_DT_VARIABLE));
 }
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_acc_visitor.hpp b/src/codegen/codegen_acc_visitor.hpp
index 1a3f60503f..dd5c337a9a 100644
--- a/src/codegen/codegen_acc_visitor.hpp
+++ b/src/codegen/codegen_acc_visitor.hpp
@@ -15,8 +15,7 @@
 #include "codegen/codegen_cpp_visitor.hpp"
 
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 /**
  * \addtogroup codegen_backends
@@ -116,13 +115,13 @@ class CodegenAccVisitor: public CodegenCppVisitor {
     void print_net_send_buf_update_to_host() const override;
 
     /// update NetSendBuffer_t count from host to device
-    virtual void print_net_send_buf_count_update_to_device() const override;
+    void print_net_send_buf_count_update_to_device() const override;
 
     /// update dt from host to device
-    virtual void print_dt_update_to_device() const override;
+    void print_dt_update_to_device() const override;
 
     // synchronise/wait on stream specific to NrnThread
-    virtual void print_device_stream_wait() const override;
+    void print_device_stream_wait() const override;
 
     /// print atomic capture pragma
     void print_device_atomic_capture_annotation() const override;
@@ -151,5 +150,4 @@ class CodegenAccVisitor: public CodegenCppVisitor {
 
 /** \} */  // end of codegen_backends
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_compatibility_visitor.cpp b/src/codegen/codegen_compatibility_visitor.cpp
index 5ed3a41963..8648116ecd 100644
--- a/src/codegen/codegen_compatibility_visitor.cpp
+++ b/src/codegen/codegen_compatibility_visitor.cpp
@@ -12,9 +12,7 @@
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
-
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 const std::map<ast::AstNodeType, CodegenCompatibilityVisitor::FunctionPointer>
     CodegenCompatibilityVisitor::unhandled_ast_types_func(
@@ -101,7 +99,7 @@ std::string CodegenCompatibilityVisitor::return_error_if_no_bbcore_read_write(
         parser::CDriver driver;
 
         driver.scan_string(verbatim_statement_string);
-        auto tokens = driver.all_tokens();
+        const auto& tokens = driver.all_tokens();
 
         for (const auto& token: tokens) {
             if (token == "bbcore_read") {
@@ -132,7 +130,7 @@ std::string CodegenCompatibilityVisitor::return_error_if_no_bbcore_read_write(
 bool CodegenCompatibilityVisitor::find_unhandled_ast_nodes(Ast& node) const {
     std::vector<ast::AstNodeType> unhandled_ast_types;
     unhandled_ast_types.reserve(unhandled_ast_types_func.size());
-    for (auto [node_type, _]: unhandled_ast_types_func) {
+    for (const auto& [node_type, _]: unhandled_ast_types_func) {
         unhandled_ast_types.push_back(node_type);
     }
     const auto& unhandled_ast_nodes = collect_nodes(node, unhandled_ast_types);
@@ -158,5 +156,4 @@ bool CodegenCompatibilityVisitor::find_unhandled_ast_nodes(Ast& node) const {
     return false;
 }
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_compatibility_visitor.hpp b/src/codegen/codegen_compatibility_visitor.hpp
index 311c540efb..0a3f2a5947 100644
--- a/src/codegen/codegen_compatibility_visitor.hpp
+++ b/src/codegen/codegen_compatibility_visitor.hpp
@@ -22,8 +22,7 @@
 #include "utils/logger.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 using namespace ast;
 
@@ -157,5 +156,4 @@ class CodegenCompatibilityVisitor: public visitor::AstVisitor {
 
 /** \} */  // end of codegen_backends
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_cpp_visitor.cpp b/src/codegen/codegen_cpp_visitor.cpp
index e661f5685b..762503a34e 100644
--- a/src/codegen/codegen_cpp_visitor.cpp
+++ b/src/codegen/codegen_cpp_visitor.cpp
@@ -28,8 +28,7 @@
 #include "visitors/var_usage_visitor.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 using namespace ast;
 
@@ -529,12 +528,6 @@ std::string CodegenCppVisitor::breakpoint_current(std::string current) const {
     return current;
 }
 
-
-int CodegenCppVisitor::float_variables_size() const {
-    return codegen_float_variables.size();
-}
-
-
 int CodegenCppVisitor::int_variables_size() const {
     const auto count_semantics = [](int sum, const IndexSemantics& sem) { return sum += sem.size; };
     return std::accumulate(info.semantics.begin(), info.semantics.end(), 0, count_semantics);
@@ -554,23 +547,22 @@ std::vector<std::string> CodegenCppVisitor::ion_read_statements(BlockType type)
     }
     std::vector<std::string> statements;
     for (const auto& ion: info.ions) {
-        auto name = ion.name;
         for (const auto& var: ion.reads) {
             auto const iter = std::find(ion.implicit_reads.begin(), ion.implicit_reads.end(), var);
             if (iter != ion.implicit_reads.end()) {
                 continue;
             }
-            auto variable_names = read_ion_variable_name(var);
-            auto first = get_variable_name(variable_names.first);
-            auto second = get_variable_name(variable_names.second);
-            statements.push_back(fmt::format("{} = {};", first, second));
+            const auto& [dest, src] = read_ion_variable_name(var);
+            auto dest_var = get_variable_name(dest);
+            auto src_var = get_variable_name(src);
+            statements.push_back(fmt::format("{} = {};", dest_var, src_var));
         }
         for (const auto& var: ion.writes) {
             if (ion.is_ionic_conc(var)) {
-                auto variables = read_ion_variable_name(var);
-                auto first = get_variable_name(variables.first);
-                auto second = get_variable_name(variables.second);
-                statements.push_back(fmt::format("{} = {};", first, second));
+                const auto& [dest, src] = read_ion_variable_name(var);
+                auto dest_var = get_variable_name(dest);
+                auto src_var = get_variable_name(src);
+                statements.push_back(fmt::format("{} = {};", dest_var, src_var));
             }
         }
     }
@@ -578,33 +570,55 @@ std::vector<std::string> CodegenCppVisitor::ion_read_statements(BlockType type)
 }
 
 
-std::vector<std::string> CodegenCppVisitor::ion_read_statements_optimized(BlockType type) const {
+std::vector<std::string> CodegenCppVisitor::ion_read_statements_optimized(BlockType /* type */) const {
     std::vector<std::string> statements;
     for (const auto& ion: info.ions) {
         for (const auto& var: ion.writes) {
             if (ion.is_ionic_conc(var)) {
-                auto variables = read_ion_variable_name(var);
-                auto first = "ionvar." + variables.first;
-                const auto& second = get_variable_name(variables.second);
-                statements.push_back(fmt::format("{} = {};", first, second));
+                const auto& [dest, src] = read_ion_variable_name(var);
+                auto dest_var = "ionvar." + dest;
+                const auto& src_var = get_variable_name(src);
+                statements.push_back(fmt::format("{} = {};", dest_var, src_var));
             }
         }
     }
     return statements;
 }
 
+
+void CodegenCppVisitor::handle_initial_ion_write_statement(const Ion& ion,
+                                               const std::string& concentration,
+                                               std::vector<ShadowUseStatement>& statements) const {
+    int index = 0;
+    if (ion.is_intra_cell_conc(concentration)) {
+        index = 1;
+    } else if (ion.is_extra_cell_conc(concentration)) {
+        index = 2;
+    } else {
+        /// \todo Unhandled case in neuron implementation
+        throw std::logic_error(fmt::format("codegen error for {} ion", ion.name));
+    }
+    auto ion_type_name = fmt::format("{}_type", ion.name);
+    auto lhs = fmt::format("int {}", ion_type_name);
+    auto op = "=";
+    auto rhs = get_variable_name(ion_type_name);
+    statements.push_back(ShadowUseStatement{lhs, op, rhs});
+    auto statement = conc_write_statement(ion.name, concentration, index);
+    statements.push_back(ShadowUseStatement{statement, "", ""});
+
+}
+
 // NOLINTNEXTLINE(readability-function-cognitive-complexity)
-std::vector<ShadowUseStatement> CodegenCppVisitor::ion_write_statements(BlockType type) {
+std::vector<ShadowUseStatement> CodegenCppVisitor::ion_write_statements(BlockType type) const {
     std::vector<ShadowUseStatement> statements;
     for (const auto& ion: info.ions) {
         std::string concentration;
-        auto name = ion.name;
         for (const auto& var: ion.writes) {
-            auto variable_names = write_ion_variable_name(var);
+            const auto& [dest, src] = write_ion_variable_name(var);
             if (ion.is_ionic_current(var)) {
                 if (type == BlockType::Equation) {
                     auto current = breakpoint_current(var);
-                    auto lhs = variable_names.first;
+                    const auto& lhs = dest;
                     auto op = "+=";
                     auto rhs = get_variable_name(current);
                     if (info.point_process) {
@@ -617,30 +631,15 @@ std::vector<ShadowUseStatement> CodegenCppVisitor::ion_write_statements(BlockTyp
                 if (!ion.is_rev_potential(var)) {
                     concentration = var;
                 }
-                auto lhs = variable_names.first;
+                const auto& lhs = dest;
                 auto op = "=";
-                auto rhs = get_variable_name(variable_names.second);
+                const auto& rhs = get_variable_name(src);
                 statements.push_back(ShadowUseStatement{lhs, op, rhs});
             }
         }
 
         if (type == BlockType::Initial && !concentration.empty()) {
-            int index = 0;
-            if (ion.is_intra_cell_conc(concentration)) {
-                index = 1;
-            } else if (ion.is_extra_cell_conc(concentration)) {
-                index = 2;
-            } else {
-                /// \todo Unhandled case in neuron implementation
-                throw std::logic_error(fmt::format("codegen error for {} ion", ion.name));
-            }
-            auto ion_type_name = fmt::format("{}_type", ion.name);
-            auto lhs = fmt::format("int {}", ion_type_name);
-            auto op = "=";
-            auto rhs = get_variable_name(ion_type_name);
-            statements.push_back(ShadowUseStatement{lhs, op, rhs});
-            auto statement = conc_write_statement(ion.name, concentration, index);
-            statements.push_back(ShadowUseStatement{statement, "", ""});
+            handle_initial_ion_write_statement(ion, concentration, statements);
         }
     }
     return statements;
@@ -742,7 +741,7 @@ void CodegenCppVisitor::update_index_semantics() {
             info.semantics.emplace_back(index++, fmt::format("#{}_ion", ion.name), 1);
         }
     }
-    for (auto& var: info.pointer_variables) {
+    for (const auto& var: info.pointer_variables) {
         if (info.first_pointer_var_index == -1) {
             info.first_pointer_var_index = index;
         }
@@ -1373,8 +1372,6 @@ void CodegenCppVisitor::print_function_prototypes() {
 
 
 static const TableStatement* get_table_statement(const ast::Block& node) {
-    // TableStatementVisitor v;
-
     const auto& table_statements = collect_nodes(node, {AstNodeType::TABLE_STATEMENT});
 
     if (table_statements.size() != 1) {
@@ -1387,7 +1384,7 @@ static const TableStatement* get_table_statement(const ast::Block& node) {
 }
 
 
-std::tuple<bool, int> CodegenCppVisitor::check_if_var_is_array(const std::string& name) {
+std::tuple<bool, int> CodegenCppVisitor::check_if_var_is_array(const std::string& name) const {
     auto symbol = program_symtab->lookup_in_scope(name);
     if (!symbol) {
         throw std::runtime_error(
@@ -1403,8 +1400,8 @@ std::tuple<bool, int> CodegenCppVisitor::check_if_var_is_array(const std::string
 
 void CodegenCppVisitor::print_table_check_function(const Block& node) {
     auto statement = get_table_statement(node);
-    auto table_variables = statement->get_table_vars();
-    auto depend_variables = statement->get_depend_vars();
+    const auto& table_variables = statement->get_table_vars();
+    const auto& depend_variables = statement->get_depend_vars();
     const auto& from = statement->get_from();
     const auto& to = statement->get_to();
     auto name = node.get_node_name();
@@ -1413,7 +1410,6 @@ void CodegenCppVisitor::print_table_check_function(const Block& node) {
     auto use_table_var = get_variable_name(naming::USE_TABLE_VARIABLE);
     auto tmin_name = get_variable_name("tmin_" + name);
     auto mfac_name = get_variable_name("mfac_" + name);
-    auto float_type = default_float_data_type();
 
     printer->add_newline(2);
     print_device_method_annotation();
@@ -1427,7 +1423,7 @@ void CodegenCppVisitor::print_table_check_function(const Block& node) {
 
         printer->add_line("static bool make_table = true;");
         for (const auto& variable: depend_variables) {
-            printer->fmt_line("static {} save_{};", float_type, variable->get_node_name());
+            printer->fmt_line("static {} save_{};", default_float_data_type(), variable->get_node_name());
         }
 
         for (const auto& variable: depend_variables) {
@@ -1922,7 +1918,7 @@ void CodegenCppVisitor::print_eigen_linear_solver(const std::string& float_type,
 /****************************************************************************************/
 
 
-std::string CodegenCppVisitor::internal_method_arguments() {
+std::string CodegenCppVisitor::internal_method_arguments() const {
     if (ion_variable_struct_required()) {
         return "id, pnodecount, inst, ionvar, data, indexes, thread, nt, v";
     }
@@ -1933,7 +1929,7 @@ std::string CodegenCppVisitor::internal_method_arguments() {
 /**
  * @todo: figure out how to correctly handle qualifiers
  */
-CodegenCppVisitor::ParamVector CodegenCppVisitor::internal_method_parameters() {
+CodegenCppVisitor::ParamVector CodegenCppVisitor::internal_method_parameters() const {
     ParamVector params;
     params.emplace_back("", "int", "", "id");
     params.emplace_back("", "int", "", "pnodecount");
@@ -1977,7 +1973,7 @@ std::string CodegenCppVisitor::nrn_thread_arguments() const {
  * Function call arguments when function or procedure is defined in the
  * same mod file itself
  */
-std::string CodegenCppVisitor::nrn_thread_internal_arguments() {
+std::string CodegenCppVisitor::nrn_thread_internal_arguments() const {
     if (ion_variable_struct_required()) {
         return "id, pnodecount, inst, ionvar, data, indexes, thread, nt, v";
     }
@@ -2076,7 +2072,7 @@ std::pair<std::string, std::string> CodegenCppVisitor::write_ion_variable_name(
 
 std::string CodegenCppVisitor::conc_write_statement(const std::string& ion_name,
                                                     const std::string& concentration,
-                                                    int index) {
+                                                    int index) const {
     auto conc_var_name = get_variable_name(naming::ION_VARNAME_PREFIX + concentration);
     auto style_var_name = get_variable_name("style_" + ion_name);
     return fmt::format(
@@ -2103,7 +2099,7 @@ std::string CodegenCppVisitor::conc_write_statement(const std::string& ion_name,
  * to queue that will be used in reduction queue.
  */
 std::string CodegenCppVisitor::process_shadow_update_statement(const ShadowUseStatement& statement,
-                                                               BlockType /* type */) {
+                                                               BlockType /* type */) const {
     // when there is no operator or rhs then that statement doesn't need shadow update
     if (statement.op.empty() && statement.rhs.empty()) {
         auto text = statement.lhs + ";";
@@ -2525,7 +2521,7 @@ void CodegenCppVisitor::print_mechanism_global_var_structure(bool print_initiali
     // is false. But as v is always local variable and passed as argument,
     // we don't need to use global variable v
 
-    auto& top_locals = info.top_local_variables;
+    const auto& top_locals = info.top_local_variables;
     if (!info.vectorize && !top_locals.empty()) {
         for (const auto& var: top_locals) {
             auto name = var->get_name();
@@ -2587,7 +2583,7 @@ void CodegenCppVisitor::print_mechanism_global_var_structure(bool print_initiali
 
     for (const auto& var: info.constant_variables) {
         auto const name = var->get_name();
-        auto* const value_ptr = var->get_value().get();
+        const auto* const value_ptr = var->get_value().get();
         double const value{value_ptr ? *value_ptr : 0};
         printer->fmt_line("{}{} {}{};",
                           qualifier,
@@ -3075,13 +3071,13 @@ void CodegenCppVisitor::print_mechanism_range_var_structure(bool print_initializ
                           print_initializers ? fmt::format("{{&coreneuron::{}}}", name)
                                              : std::string{});
     }
-    for (auto& var: codegen_float_variables) {
+    for (const auto& var: codegen_float_variables) {
         const auto& name = var->get_name();
         auto type = get_range_var_float_type(var);
         auto qualifier = is_constant_variable(name) ? "const " : "";
         printer->fmt_line("{}{}* {}{};", qualifier, type, name, value_initialize);
     }
-    for (auto& var: codegen_int_variables) {
+    for (const auto& var: codegen_int_variables) {
         const auto& name = var.symbol->get_name();
         if (var.is_index || var.is_integer) {
             auto qualifier = var.is_constant ? "const " : "";
@@ -3179,7 +3175,7 @@ void CodegenCppVisitor::print_setup_range_variable() {
  * are pointers to internal variables (e.g. ions). Hence, we check if given
  * variable can be safely converted to new type. If so, return new type.
  */
-std::string CodegenCppVisitor::get_range_var_float_type(const SymbolType& symbol) {
+std::string CodegenCppVisitor::get_range_var_float_type(const SymbolType& symbol) const {
     // clang-format off
     auto with   =   NmodlType::read_ion_var
                     | NmodlType::write_ion_var
@@ -3283,7 +3279,7 @@ void CodegenCppVisitor::print_instance_variable_setup() {
         id += var->get_length();
     }
 
-    for (auto& var: codegen_int_variables) {
+    for (const auto& var: codegen_int_variables) {
         auto name = var.symbol->get_name();
         auto const variable = [&var]() {
             if (var.is_index || var.is_integer) {
@@ -3341,9 +3337,9 @@ void CodegenCppVisitor::print_initial_block(const InitialBlock* node) {
     }
 
     // write ion statements
-    auto write_statements = ion_write_statements(BlockType::Initial);
-    for (auto& statement: write_statements) {
-        auto text = process_shadow_update_statement(statement, BlockType::Initial);
+    const auto& write_statements = ion_write_statements(BlockType::Initial);
+    for (const auto& statement: write_statements) {
+        const auto& text = process_shadow_update_statement(statement, BlockType::Initial);
         printer->add_line(text);
     }
 }
@@ -3748,8 +3744,8 @@ void CodegenCppVisitor::print_net_receive_common_code(const Block& node, bool ne
     if (!parameters.empty()) {
         int i = 0;
         printer->add_newline();
-        for (auto& parameter: parameters) {
-            auto name = parameter->get_node_name();
+        for (const auto& parameter: parameters) {
+            const auto& name = parameter->get_node_name();
             bool var_used = VarUsageVisitor().variable_used(node, "(*" + name + ")");
             if (var_used) {
                 printer->fmt_line("double* {} = weights + weight_index + {};", name, i);
@@ -4363,7 +4359,7 @@ void CodegenCppVisitor::print_nrn_current(const BreakpointBlock& node) {
                                     get_parameter_str(args));
     printer->add_line("double current = 0.0;");
     print_statement_block(*block, false, false);
-    for (auto& current: info.currents) {
+    for (const auto& current: info.currents) {
         const auto& name = get_variable_name(current);
         printer->fmt_line("current += {};", name);
     }
@@ -4409,12 +4405,12 @@ void CodegenCppVisitor::print_nrn_cur_conductance_kernel(const BreakpointBlock&
 }
 
 
-void CodegenCppVisitor::print_nrn_cur_non_conductance_kernel() {
+void CodegenCppVisitor::print_nrn_cur_non_conductance_kernel() const {
     printer->fmt_line("double g = nrn_current_{}({}+0.001);",
                                   info.mod_suffix,
                                   internal_method_arguments());
-    for (auto& ion: info.ions) {
-        for (auto& var: ion.writes) {
+    for (const auto& ion: info.ions) {
+        for (const auto& var: ion.writes) {
             if (ion.is_ionic_current(var)) {
                 const auto& name = get_variable_name(var);
                 printer->fmt_line("double di{} = {};", ion.name, name);
@@ -4687,5 +4683,4 @@ void CodegenCppVisitor::visit_program(const Program& node) {
     print_codegen_routines();
 }
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_cpp_visitor.hpp b/src/codegen/codegen_cpp_visitor.hpp
index ee0344058c..2b729d81cb 100644
--- a/src/codegen/codegen_cpp_visitor.hpp
+++ b/src/codegen/codegen_cpp_visitor.hpp
@@ -33,9 +33,7 @@
 
 
 /// encapsulates code generation backend implementations
-namespace nmodl {
-
-namespace codegen {
+namespace nmodl::codegen {
 
 /**
  * \defgroup codegen Code Generation Implementation
@@ -498,7 +496,9 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
     /**
      * Number of float variables in the model
      */
-    int float_variables_size() const;
+    auto float_variables_size() const {
+        return codegen_float_variables.size();
+    }
 
 
     /**
@@ -733,9 +733,12 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      * \param type The type of code block being generated
      * \return     A \c vector of strings representing the write-back of ion variables
      */
-    std::vector<ShadowUseStatement> ion_write_statements(BlockType type);
+    std::vector<ShadowUseStatement> ion_write_statements(BlockType type) const;
 
 
+    void handle_initial_ion_write_statement(const Ion& ion,
+                                       const std::string& concentration,
+                                       std::vector<ShadowUseStatement>& statements) const;
     /**
      * Return ion variable name and corresponding ion read variable name
      * \param name The ion variable name
@@ -761,21 +764,21 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      */
     std::string conc_write_statement(const std::string& ion_name,
                                      const std::string& concentration,
-                                     int index);
+                                     int index) const;
 
 
     /**
      * Arguments for functions that are defined and used internally.
      * \return the method arguments
      */
-    std::string internal_method_arguments();
+    std::string internal_method_arguments() const;
 
 
     /**
      * Parameters for internally defined functions
      * \return the method parameters
      */
-    ParamVector internal_method_parameters();
+    ParamVector internal_method_parameters() const;
 
 
     /**
@@ -812,7 +815,7 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
     /**
      * Arguments for "_threadargs_" macro in neuron implementation
      */
-    std::string nrn_thread_internal_arguments();
+    std::string nrn_thread_internal_arguments() const;
 
 
     /**
@@ -956,7 +959,7 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      * \return \c return a tuple <true, array_length> if variable
      *            is an array otherwise <false, 0>
      */
-    std::tuple<bool, int> check_if_var_is_array(const std::string& name);
+    std::tuple<bool, int> check_if_var_is_array(const std::string& name) const;
 
     /**
      * Print declaration of macro NRN_PRCELLSTATE for debugging
@@ -1002,7 +1005,7 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      * Returns floating point type for given range variable symbol
      * \param symbol A range variable symbol
      */
-    std::string get_range_var_float_type(const SymbolType& symbol);
+    std::string get_range_var_float_type(const SymbolType& symbol) const;
 
 
     /**
@@ -1407,7 +1410,7 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      * \return          The generated target backend code
      */
     std::string process_shadow_update_statement(const ShadowUseStatement& statement,
-                                                BlockType type);
+                                                BlockType type) const;
 
 
     /**
@@ -1434,7 +1437,7 @@ class CodegenCppVisitor: public visitor::ConstAstVisitor {
      * If the NMODL \c conductance keyword is \b not used in the \c breakpoint block, then
      * CodegenCppVisitor::print_nrn_cur_kernel will use this printer
      */
-    void print_nrn_cur_non_conductance_kernel();
+    void print_nrn_cur_non_conductance_kernel() const;
 
 
     /**
@@ -1865,5 +1868,4 @@ void CodegenCppVisitor::print_function_declaration(const T& node, const std::str
 
 /** \} */  // end of codegen_backends
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_helper_visitor.cpp b/src/codegen/codegen_helper_visitor.cpp
index fa9e4438b6..40ed8c0785 100644
--- a/src/codegen/codegen_helper_visitor.cpp
+++ b/src/codegen/codegen_helper_visitor.cpp
@@ -16,8 +16,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 using namespace ast;
 
@@ -774,5 +773,4 @@ void CodegenHelperVisitor::visit_after_block(const ast::AfterBlock& node) {
     info.before_after_blocks.push_back(&node);
 }
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_helper_visitor.hpp b/src/codegen/codegen_helper_visitor.hpp
index b960bdc06f..daf483e461 100644
--- a/src/codegen/codegen_helper_visitor.hpp
+++ b/src/codegen/codegen_helper_visitor.hpp
@@ -18,8 +18,7 @@
 #include "symtab/symbol_table.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 /**
  * @addtogroup codegen_details
@@ -119,5 +118,4 @@ class CodegenHelperVisitor: public visitor::ConstAstVisitor {
 
 /** @} */  // end of codegen_details
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_info.cpp b/src/codegen/codegen_info.cpp
index b7d40125a6..b5a2dcff69 100644
--- a/src/codegen/codegen_info.cpp
+++ b/src/codegen/codegen_info.cpp
@@ -12,8 +12,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 using visitor::VarUsageVisitor;
 
@@ -106,5 +105,4 @@ bool CodegenInfo::is_voltage_used_by_watch_statements() const {
     });
 }
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_info.hpp b/src/codegen/codegen_info.hpp
index 67cf6c9bb4..b3bcb19bf9 100644
--- a/src/codegen/codegen_info.hpp
+++ b/src/codegen/codegen_info.hpp
@@ -20,8 +20,7 @@
 #include "ast/ast.hpp"
 #include "symtab/symbol_table.hpp"
 
-namespace nmodl {
-namespace codegen {
+namespace nmodl::codegen {
 
 /**
  * \addtogroup codegen_details
@@ -439,5 +438,4 @@ struct CodegenInfo {
 
 /** \} */  // end of codegen_backends
 
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen
diff --git a/src/codegen/codegen_naming.hpp b/src/codegen/codegen_naming.hpp
index 3af8a49e88..c56af84218 100644
--- a/src/codegen/codegen_naming.hpp
+++ b/src/codegen/codegen_naming.hpp
@@ -11,10 +11,7 @@
 #include <string>
 
 
-namespace nmodl {
-namespace codegen {
-/// different variable names used in code generation
-namespace naming {
+namespace nmodl::codegen::naming {
 
 /// nmodl language version
 /// @todo : should be moved from codegen to global scope
@@ -179,6 +176,4 @@ static constexpr char ION_VARNAME_PREFIX[] = "ion_";
                 {"_tqitem", "tqitem"}};
 // clang-format on
 
-}  // namespace naming
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen::naming
diff --git a/src/codegen/codegen_utils.cpp b/src/codegen/codegen_utils.cpp
index 5f7b623239..1567c12c9a 100644
--- a/src/codegen/codegen_utils.cpp
+++ b/src/codegen/codegen_utils.cpp
@@ -9,9 +9,7 @@
 
 #include "codegen/codegen_cpp_visitor.hpp"
 
-namespace nmodl {
-namespace codegen {
-namespace utils {
+namespace nmodl::codegen::utils {
 /**
  * \details We can directly print value but if user specify value as integer then
  * then it gets printed as an integer. To avoid this, we use below wrappers.
@@ -38,6 +36,4 @@ std::string format_float_string<CodegenCppVisitor>(const std::string& s_value) {
     }
     return s_value;
 }
-}  // namespace utils
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen::utils
diff --git a/src/codegen/codegen_utils.hpp b/src/codegen/codegen_utils.hpp
index 4c910b36b5..f817eb8c58 100644
--- a/src/codegen/codegen_utils.hpp
+++ b/src/codegen/codegen_utils.hpp
@@ -15,9 +15,7 @@
 
 #include <string>
 
-namespace nmodl {
-namespace codegen {
-namespace utils {
+namespace nmodl::codegen::utils {
 
 /**
  * Handles the double constants format being printed in the generated code.
@@ -46,6 +44,4 @@ std::string format_double_string(const std::string& s_value);
 template <typename T>
 std::string format_float_string(const std::string& s_value);
 
-}  // namespace utils
-}  // namespace codegen
-}  // namespace nmodl
+}  // namespace nmodl::codegen::utils
diff --git a/src/language/nodes.py b/src/language/nodes.py
index fc45edf181..4e440b884f 100644
--- a/src/language/nodes.py
+++ b/src/language/nodes.py
@@ -196,13 +196,17 @@ def get_typename(self):
 
         return type_name
 
+    @classmethod
+    def add_const_rvalue_reference(cls, type):
+        return f"const {type}&"
+
     def get_rvalue_typename(self):
         """returns rvalue reference type of the node"""
         typename = self.get_typename()
         if self.is_vector:
-            return "const " + typename + "&"
+            return self.add_const_rvalue_reference(typename)
         if self.is_base_type_node and not self.is_integral_type_node or self.is_ptr_excluded_node:
-            return "const " + typename + "&"
+            return self.add_const_rvalue_reference(typename)
         return typename
 
     def get_shared_typename(self):
@@ -245,7 +249,7 @@ def member_rvalue_typename(self):
         """returns rvalue reference type when used as returned or parameter type"""
         typename = self.member_typename
         if not self.is_integral_type_node:
-            return "const " + typename + "&"
+            return self.add_const_rvalue_reference(typename)
         return typename
 
     def get_add_methods_declaration(self):
diff --git a/src/lexer/c11_lexer.hpp b/src/lexer/c11_lexer.hpp
index b95c1baf95..117f9d7b2e 100644
--- a/src/lexer/c11_lexer.hpp
+++ b/src/lexer/c11_lexer.hpp
@@ -28,8 +28,7 @@
 #include "FlexLexer.h"
 #endif
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * @addtogroup lexer
@@ -108,5 +107,4 @@ class CLexer: public CFlexLexer {
 
 /** @} */  // end of lexer
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/lexer/diffeq_lexer.hpp b/src/lexer/diffeq_lexer.hpp
index bf6202aac7..ef39abe50e 100644
--- a/src/lexer/diffeq_lexer.hpp
+++ b/src/lexer/diffeq_lexer.hpp
@@ -28,8 +28,7 @@
 #include "FlexLexer.h"
 #endif
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * @addtogroup lexer
@@ -80,5 +79,4 @@ class DiffeqLexer: public DiffEqFlexLexer {
 
 /** @} */  // end of lexer
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/lexer/nmodl_lexer.hpp b/src/lexer/nmodl_lexer.hpp
index e89db2a04c..1a135800cc 100644
--- a/src/lexer/nmodl_lexer.hpp
+++ b/src/lexer/nmodl_lexer.hpp
@@ -35,8 +35,7 @@
 #include "FlexLexer.h"
 #endif
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * @defgroup lexer Lexer Implementation
@@ -154,5 +153,4 @@ class NmodlLexer: public NmodlFlexLexer {
 
 /** @} */  // end of lexer
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/lexer/unit_lexer.hpp b/src/lexer/unit_lexer.hpp
index c7651c3137..839b017a44 100644
--- a/src/lexer/unit_lexer.hpp
+++ b/src/lexer/unit_lexer.hpp
@@ -28,8 +28,7 @@
 #include "FlexLexer.h"
 #endif
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * @addtogroup lexer
@@ -83,5 +82,4 @@ class UnitLexer: public UnitFlexLexer {
     virtual UnitParser::symbol_type next_token();
 };
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/c11_driver.cpp b/src/parser/c11_driver.cpp
index a48799d7d8..d9d1559f84 100644
--- a/src/parser/c11_driver.cpp
+++ b/src/parser/c11_driver.cpp
@@ -11,8 +11,7 @@
 #include "lexer/c11_lexer.hpp"
 #include "parser/c11_driver.hpp"
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 CDriver::CDriver() = default;
 
@@ -75,5 +74,4 @@ void CDriver::scan_string(const std::string& text) {
     }
 }
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/c11_driver.hpp b/src/parser/c11_driver.hpp
index 555f6a5050..c9558266e2 100644
--- a/src/parser/c11_driver.hpp
+++ b/src/parser/c11_driver.hpp
@@ -14,8 +14,7 @@
 #include <vector>
 
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /// flex generated scanner class (extends base lexer class of flex)
 class CLexer;
@@ -109,5 +108,4 @@ class CDriver {
 
 /** \} */  // end of parser
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/diffeq_context.cpp b/src/parser/diffeq_context.cpp
index 298b2185d9..7cbc5239c7 100644
--- a/src/parser/diffeq_context.cpp
+++ b/src/parser/diffeq_context.cpp
@@ -11,9 +11,7 @@
 #include "utils/string_utils.hpp"
 
 
-namespace nmodl {
-namespace parser {
-namespace diffeq {
+namespace nmodl::parser::diffeq {
 
 Term::Term(const std::string& expr, const std::string& state)
     : expr(expr)
@@ -182,6 +180,4 @@ std::string DiffEqContext::get_solution(bool& cnexp_possible) {
     return solution;
 }
 
-}  // namespace diffeq
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser::diffeq
diff --git a/src/parser/diffeq_context.hpp b/src/parser/diffeq_context.hpp
index 08fde3a300..eb83d5eeb0 100644
--- a/src/parser/diffeq_context.hpp
+++ b/src/parser/diffeq_context.hpp
@@ -10,9 +10,7 @@
 #include <string>
 #include <utility>
 
-namespace nmodl {
-namespace parser {
-namespace diffeq {
+namespace nmodl::parser::diffeq {
 
 /**
  * \class Term
@@ -127,6 +125,4 @@ class DiffEqContext {
     void print() const;
 };
 
-}  // namespace diffeq
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser::diffeq
diff --git a/src/parser/diffeq_driver.cpp b/src/parser/diffeq_driver.cpp
index 5cf92a1ca6..7b4dc6072e 100644
--- a/src/parser/diffeq_driver.cpp
+++ b/src/parser/diffeq_driver.cpp
@@ -12,8 +12,7 @@
 #include "parser/diffeq_driver.hpp"
 #include "utils/string_utils.hpp"
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 void DiffeqDriver::parse_equation(const std::string& equation,
                                   std::string& state,
@@ -71,5 +70,4 @@ bool DiffeqDriver::cnexp_possible(const std::string& equation, std::string& solu
     return cnexp_possible;
 }
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/diffeq_driver.hpp b/src/parser/diffeq_driver.hpp
index 2162cf41c9..a247913dd8 100644
--- a/src/parser/diffeq_driver.hpp
+++ b/src/parser/diffeq_driver.hpp
@@ -12,8 +12,7 @@
 #include "parser/diffeq_context.hpp"
 
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /// flex generated scanner class (extends base lexer class of flex)
 class DiffeqlLexer;
@@ -60,5 +59,4 @@ class DiffeqDriver {
 
 /** @} */  // end of parser
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/diffeq_helper.hpp b/src/parser/diffeq_helper.hpp
index c04111d788..55041625a8 100644
--- a/src/parser/diffeq_helper.hpp
+++ b/src/parser/diffeq_helper.hpp
@@ -9,9 +9,6 @@
 
 #include "parser/diffeq_context.hpp"
 
-namespace nmodl {
-namespace parser {
-
 /**
  * \brief Helper functions for solving differential equations
  *
@@ -23,7 +20,7 @@ namespace parser {
  * Need to revisit this, may be using better library like symengine
  * altogether.
  */
-namespace diffeq {
+ namespace nmodl::parser::diffeq {
 
 /// operators beign supported as part of binary expressions
 enum class MathOp { add = 1, sub, mul, div };
@@ -175,6 +172,4 @@ inline Term eval_derivative<MathOp::div>(const Term& first,
     return solution;
 }
 
-}  // namespace diffeq
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser::diffeq
diff --git a/src/parser/nmodl_driver.cpp b/src/parser/nmodl_driver.cpp
index 63f50cc3a5..c803e11b01 100644
--- a/src/parser/nmodl_driver.cpp
+++ b/src/parser/nmodl_driver.cpp
@@ -15,8 +15,7 @@
 
 namespace fs = std::filesystem;
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 NmodlDriver::NmodlDriver(bool strace, bool ptrace)
     : trace_scanner(strace)
@@ -164,5 +163,4 @@ std::string NmodlDriver::check_include_argument(const location& location,
     return filename.substr(1, filename.size() - 2);
 }
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/nmodl_driver.hpp b/src/parser/nmodl_driver.hpp
index 217879b053..304b0d2e1c 100644
--- a/src/parser/nmodl_driver.hpp
+++ b/src/parser/nmodl_driver.hpp
@@ -23,9 +23,7 @@
 
 
 /// encapsulates everything related to NMODL code generation framework
-namespace nmodl {
-/// encapsulate lexer and parsers implementations
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * \defgroup parser Parser Implementation
@@ -162,5 +160,4 @@ class NmodlDriver {
 
 /** \} */  // end of parser
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/unit_driver.cpp b/src/parser/unit_driver.cpp
index 5f709b6398..0b286fe0dd 100644
--- a/src/parser/unit_driver.cpp
+++ b/src/parser/unit_driver.cpp
@@ -11,8 +11,7 @@
 #include "lexer/unit_lexer.hpp"
 #include "parser/unit_driver.hpp"
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /// parse Units file provided as istream
 bool UnitDriver::parse_stream(std::istream& in) {
@@ -42,5 +41,4 @@ bool UnitDriver::parse_string(const std::string& input) {
     return parse_stream(iss);
 }
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/unit_driver.hpp b/src/parser/unit_driver.hpp
index 31f882e731..ee939ceacf 100644
--- a/src/parser/unit_driver.hpp
+++ b/src/parser/unit_driver.hpp
@@ -14,8 +14,7 @@
 #include <string>
 #include <vector>
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /// flex generated scanner class (extends base lexer class of flex)
 class UnitLexer;
@@ -75,5 +74,4 @@ class UnitDriver {
     }
 };
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
diff --git a/src/parser/verbatim_driver.hpp b/src/parser/verbatim_driver.hpp
index bd005879af..d7b18d716b 100644
--- a/src/parser/verbatim_driver.hpp
+++ b/src/parser/verbatim_driver.hpp
@@ -10,8 +10,7 @@
 #include <iostream>
 
 
-namespace nmodl {
-namespace parser {
+namespace nmodl::parser {
 
 /**
  * @addtogroup parser
@@ -47,8 +46,7 @@ class VerbatimDriver {
 
 /** @} */  // end of parser
 
-}  // namespace parser
-}  // namespace nmodl
+}  // namespace nmodl::parser
 
 
 int Verbatim_parse(nmodl::parser::VerbatimDriver*);
diff --git a/src/printer/code_printer.cpp b/src/printer/code_printer.cpp
index b2e5f6d865..56156cb405 100644
--- a/src/printer/code_printer.cpp
+++ b/src/printer/code_printer.cpp
@@ -8,8 +8,7 @@
 #include "printer/code_printer.hpp"
 #include "utils/string_utils.hpp"
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 CodePrinter::CodePrinter(const std::string& filename) {
     if (filename.empty()) {
@@ -110,5 +109,4 @@ void CodePrinter::pop_block(const std::string_view& suffix, std::size_t num_newl
     add_newline(num_newlines);
 }
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/code_printer.hpp b/src/printer/code_printer.hpp
index 226562fff1..6716072d8a 100644
--- a/src/printer/code_printer.hpp
+++ b/src/printer/code_printer.hpp
@@ -22,9 +22,7 @@
 #include <sstream>
 #include <string_view>
 
-namespace nmodl {
-/// implementation of various printers
-namespace printer {
+namespace nmodl::printer {
 
 /**
  * @defgroup printer Code Printers
@@ -131,5 +129,4 @@ class CodePrinter {
 
 /** @} */  // end of printer
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/decl.hpp b/src/printer/decl.hpp
index 041b2114cb..c63d03b285 100644
--- a/src/printer/decl.hpp
+++ b/src/printer/decl.hpp
@@ -12,10 +12,8 @@
  * \brief Forward references of symbols defined in namespace nmodl::printer
  */
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 class JSONPrinter;
 
-}
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/json_printer.cpp b/src/printer/json_printer.cpp
index 0a7477afc1..d31a2dfc82 100644
--- a/src/printer/json_printer.cpp
+++ b/src/printer/json_printer.cpp
@@ -9,8 +9,7 @@
 #include "utils/logger.hpp"
 
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 /// Dump output to provided file
 JSONPrinter::JSONPrinter(const std::string& filename) {
@@ -90,5 +89,4 @@ void JSONPrinter::flush() {
     }
 }
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/json_printer.hpp b/src/printer/json_printer.hpp
index 536c112352..6f6ad347dc 100644
--- a/src/printer/json_printer.hpp
+++ b/src/printer/json_printer.hpp
@@ -18,8 +18,7 @@
 #include <iostream>
 #include <stack>
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 using json = nlohmann::json;
 
@@ -100,5 +99,4 @@ class JSONPrinter {
 
 /** @} */  // end of printer
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/nmodl_printer.cpp b/src/printer/nmodl_printer.cpp
index 2e2e4494df..6e6c90b0b5 100644
--- a/src/printer/nmodl_printer.cpp
+++ b/src/printer/nmodl_printer.cpp
@@ -8,8 +8,7 @@
 #include "printer/nmodl_printer.hpp"
 #include "utils/string_utils.hpp"
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 NMODLPrinter::NMODLPrinter(const std::string& filename) {
     if (filename.empty()) {
@@ -51,5 +50,4 @@ void NMODLPrinter::pop_level() {
     *result << "}";
 }
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/printer/nmodl_printer.hpp b/src/printer/nmodl_printer.hpp
index 5d00725465..544cdd1346 100644
--- a/src/printer/nmodl_printer.hpp
+++ b/src/printer/nmodl_printer.hpp
@@ -17,8 +17,7 @@
 #include <memory>
 #include <sstream>
 
-namespace nmodl {
-namespace printer {
+namespace nmodl::printer {
 
 /**
  * @addtogroup printer
@@ -70,5 +69,4 @@ class NMODLPrinter {
 
 /** @} */  // end of printer
 
-}  // namespace printer
-}  // namespace nmodl
+}  // namespace nmodl::printer
diff --git a/src/pybind/docstrings.hpp b/src/pybind/docstrings.hpp
index 7fa8274826..871a0c3108 100644
--- a/src/pybind/docstrings.hpp
+++ b/src/pybind/docstrings.hpp
@@ -7,8 +7,7 @@
 
 #pragma once
 
-namespace nmodl {
-namespace docstring {
+namespace nmodl::docstring {
 
 constexpr const char* binary_op_enum() {
     return R"(
@@ -170,5 +169,4 @@ constexpr const char* parent_property() {
 )";
 }
 
-}  // namespace docstring
-}  // namespace nmodl
+}  // namespace nmodl::docstring
diff --git a/src/pybind/pybind_utils.hpp b/src/pybind/pybind_utils.hpp
index 43ad61dccd..ed14ff91bd 100644
--- a/src/pybind/pybind_utils.hpp
+++ b/src/pybind/pybind_utils.hpp
@@ -13,8 +13,7 @@
 #include <pybind11/stl.h>
 
 
-namespace pybind11 {
-namespace detail {
+namespace pybind11::detail {
 
 template <typename StringType>
 struct CopyFromPython {
@@ -88,8 +87,7 @@ class pythonibuf: public std::streambuf {
         setg(end, end, end);
     }
 };
-}  // namespace detail
-}  // namespace pybind11
+}  // namespace pybind11::details
 
 class VisitorOStreamResources {
   protected:
diff --git a/src/pybind/pyembed.cpp b/src/pybind/pyembed.cpp
index 447674a2b4..544c151529 100644
--- a/src/pybind/pyembed.cpp
+++ b/src/pybind/pyembed.cpp
@@ -15,9 +15,7 @@
 
 namespace fs = std::filesystem;
 
-namespace nmodl {
-
-namespace pybind_wrappers {
+namespace nmodl::pybind_wrappers {
 
 bool EmbeddedPythonLoader::have_wrappers() {
 #if defined(NMODL_STATIC_PYWRAPPER)
@@ -89,6 +87,4 @@ const pybind_wrap_api* EmbeddedPythonLoader::api() {
 }
 
 
-}  // namespace pybind_wrappers
-
-}  // namespace nmodl
+}  // namespace nmodl::pybind_wrappers
diff --git a/src/pybind/pyembed.hpp b/src/pybind/pyembed.hpp
index 2199d6b04c..f8f2576d44 100644
--- a/src/pybind/pyembed.hpp
+++ b/src/pybind/pyembed.hpp
@@ -14,8 +14,7 @@
 #include <string>
 #include <vector>
 
-namespace nmodl {
-namespace pybind_wrappers {
+namespace nmodl::pybind_wrappers {
 
 
 struct PythonExecutor {
@@ -182,5 +181,4 @@ class EmbeddedPythonLoader {
 
 pybind_wrap_api init_pybind_wrap_api() noexcept;
 
-}  // namespace pybind_wrappers
-}  // namespace nmodl
+}  // namespace nmodl::pybind_wrappers
diff --git a/src/pybind/wrapper.cpp b/src/pybind/wrapper.cpp
index d456e5c2d0..a331188482 100644
--- a/src/pybind/wrapper.cpp
+++ b/src/pybind/wrapper.cpp
@@ -17,8 +17,7 @@
 namespace py = pybind11;
 using namespace py::literals;
 
-namespace nmodl {
-namespace pybind_wrappers {
+namespace nmodl::pybind_wrappers {
 
 void SolveLinearSystemExecutor::operator()() {
     const auto locals = py::dict("eq_strings"_a = eq_system,
@@ -214,8 +213,7 @@ pybind_wrap_api init_pybind_wrap_api() noexcept {
     };
 }
 
-}  // namespace pybind_wrappers
-}  // namespace nmodl
+}  // namespace nmodl::pybind_wrappers
 
 
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
diff --git a/src/pybind/wrapper.cpp.orig b/src/pybind/wrapper.cpp.orig
new file mode 100644
index 0000000000..d456e5c2d0
--- /dev/null
+++ b/src/pybind/wrapper.cpp.orig
@@ -0,0 +1,223 @@
+/*
+ * Copyright 2023 Blue Brain Project, EPFL.
+ * See the top-level LICENSE file for details.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "codegen/codegen_naming.hpp"
+#include "pybind/pyembed.hpp"
+
+#include <pybind11/embed.h>
+#include <pybind11/stl.h>
+
+#include <set>
+#include <vector>
+
+namespace py = pybind11;
+using namespace py::literals;
+
+namespace nmodl {
+namespace pybind_wrappers {
+
+void SolveLinearSystemExecutor::operator()() {
+    const auto locals = py::dict("eq_strings"_a = eq_system,
+                                 "state_vars"_a = state_vars,
+                                 "vars"_a = vars,
+                                 "small_system"_a = small_system,
+                                 "do_cse"_a = elimination,
+                                 "function_calls"_a = function_calls,
+                                 "tmp_unique_prefix"_a = tmp_unique_prefix);
+    py::exec(R"(
+                from nmodl.ode import solve_lin_system
+                exception_message = ""
+                try:
+                    solutions, new_local_vars = solve_lin_system(eq_strings,
+                                                                 state_vars,
+                                                                 vars,
+                                                                 function_calls,
+                                                                 tmp_unique_prefix,
+                                                                 small_system,
+                                                                 do_cse)
+                except Exception as e:
+                    # if we fail, fail silently and return empty string
+                    solutions = [""]
+                    new_local_vars = [""]
+                    exception_message = str(e)
+                )",
+             py::globals(),
+             locals);
+    // returns a vector of solutions, i.e. new statements to add to block:
+    solutions = locals["solutions"].cast<std::vector<std::string>>();
+    // and a vector of new local variables that need to be declared in the block:
+    new_local_vars = locals["new_local_vars"].cast<std::vector<std::string>>();
+    // may also return a python exception message:
+    exception_message = locals["exception_message"].cast<std::string>();
+}
+
+
+void SolveNonLinearSystemExecutor::operator()() {
+    const auto locals = py::dict("equation_strings"_a = eq_system,
+                                 "state_vars"_a = state_vars,
+                                 "vars"_a = vars,
+                                 "function_calls"_a = function_calls);
+    py::exec(R"(
+                from nmodl.ode import solve_non_lin_system
+                exception_message = ""
+                try:
+                    solutions = solve_non_lin_system(equation_strings,
+                                                     state_vars,
+                                                     vars,
+                                                     function_calls)
+                except Exception as e:
+                    # if we fail, fail silently and return empty string
+                    solutions = [""]
+                    new_local_vars = [""]
+                    exception_message = str(e)
+                )",
+             py::globals(),
+             locals);
+    // returns a vector of solutions, i.e. new statements to add to block:
+    solutions = locals["solutions"].cast<std::vector<std::string>>();
+    // may also return a python exception message:
+    exception_message = locals["exception_message"].cast<std::string>();
+}
+
+void DiffeqSolverExecutor::operator()() {
+    const auto locals = py::dict("equation_string"_a = node_as_nmodl,
+                                 "dt_var"_a = dt_var,
+                                 "vars"_a = vars,
+                                 "use_pade_approx"_a = use_pade_approx,
+                                 "function_calls"_a = function_calls);
+
+    if (method == codegen::naming::EULER_METHOD) {
+        // replace x' = f(x) differential equation
+        // with forwards Euler timestep:
+        // x = x + f(x) * dt
+        py::exec(R"(
+                from nmodl.ode import forwards_euler2c
+                exception_message = ""
+                try:
+                    solution = forwards_euler2c(equation_string, dt_var, vars, function_calls)
+                except Exception as e:
+                    # if we fail, fail silently and return empty string
+                    solution = ""
+                    exception_message = str(e)
+            )",
+                 py::globals(),
+                 locals);
+    } else if (method == codegen::naming::CNEXP_METHOD) {
+        // replace x' = f(x) differential equation
+        // with analytic solution for x(t+dt) in terms of x(t)
+        // x = ...
+        py::exec(R"(
+                from nmodl.ode import integrate2c
+                exception_message = ""
+                try:
+                    solution = integrate2c(equation_string, dt_var, vars,
+                                           use_pade_approx)
+                except Exception as e:
+                    # if we fail, fail silently and return empty string
+                    solution = ""
+                    exception_message = str(e)
+            )",
+                 py::globals(),
+                 locals);
+    } else {
+        // nothing to do, but the caller should know.
+        return;
+    }
+    solution = locals["solution"].cast<std::string>();
+    exception_message = locals["exception_message"].cast<std::string>();
+}
+
+void AnalyticDiffExecutor::operator()() {
+    auto locals = py::dict("expressions"_a = expressions, "vars"_a = used_names_in_block);
+    py::exec(R"(
+                            from nmodl.ode import differentiate2c
+                            exception_message = ""
+                            try:
+                                rhs = expressions[-1].split("=", 1)[1]
+                                solution = differentiate2c(rhs,
+                                                           "v",
+                                                           vars,
+                                                           expressions[:-1]
+                                           )
+                            except Exception as e:
+                                # if we fail, fail silently and return empty string
+                                solution = ""
+                                exception_message = str(e)
+                        )",
+             py::globals(),
+             locals);
+    solution = locals["solution"].cast<std::string>();
+    exception_message = locals["exception_message"].cast<std::string>();
+}
+
+SolveLinearSystemExecutor* create_sls_executor_func() {
+    return new SolveLinearSystemExecutor();
+}
+
+SolveNonLinearSystemExecutor* create_nsls_executor_func() {
+    return new SolveNonLinearSystemExecutor();
+}
+
+DiffeqSolverExecutor* create_des_executor_func() {
+    return new DiffeqSolverExecutor();
+}
+
+AnalyticDiffExecutor* create_ads_executor_func() {
+    return new AnalyticDiffExecutor();
+}
+
+void destroy_sls_executor_func(SolveLinearSystemExecutor* exec) {
+    delete exec;
+}
+
+void destroy_nsls_executor_func(SolveNonLinearSystemExecutor* exec) {
+    delete exec;
+}
+
+void destroy_des_executor_func(DiffeqSolverExecutor* exec) {
+    delete exec;
+}
+
+void destroy_ads_executor_func(AnalyticDiffExecutor* exec) {
+    delete exec;
+}
+
+void initialize_interpreter_func() {
+    pybind11::initialize_interpreter(true);
+    const auto python_path_cstr = std::getenv("PYTHONPATH");
+    if (python_path_cstr) {
+        pybind11::module::import("sys").attr("path").cast<pybind11::list>().insert(
+            0, python_path_cstr);
+    }
+}
+
+void finalize_interpreter_func() {
+    pybind11::finalize_interpreter();
+}
+
+pybind_wrap_api init_pybind_wrap_api() noexcept {
+    return {
+        &nmodl::pybind_wrappers::initialize_interpreter_func,
+        &nmodl::pybind_wrappers::finalize_interpreter_func,
+        &nmodl::pybind_wrappers::create_sls_executor_func,
+        &nmodl::pybind_wrappers::create_nsls_executor_func,
+        &nmodl::pybind_wrappers::create_des_executor_func,
+        &nmodl::pybind_wrappers::create_ads_executor_func,
+        &nmodl::pybind_wrappers::destroy_sls_executor_func,
+        &nmodl::pybind_wrappers::destroy_nsls_executor_func,
+        &nmodl::pybind_wrappers::destroy_des_executor_func,
+        &nmodl::pybind_wrappers::destroy_ads_executor_func,
+    };
+}
+
+}  // namespace pybind_wrappers
+}  // namespace nmodl
+
+
+// NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
+__attribute__((visibility("default"))) nmodl::pybind_wrappers::pybind_wrap_api nmodl_wrapper_api =
+    nmodl::pybind_wrappers::init_pybind_wrap_api();
diff --git a/src/solver/crout/crout.hpp b/src/solver/crout/crout.hpp
index cf45043b72..3c5b018494 100644
--- a/src/solver/crout/crout.hpp
+++ b/src/solver/crout/crout.hpp
@@ -23,8 +23,7 @@
 #include "coreneuron/utils/offload.hpp"
 #endif
 
-namespace nmodl {
-namespace crout {
+namespace nmodl::crout {
 
 /**
  * \brief Crout matrix decomposition : in-place LU Decomposition of matrix a.
@@ -203,5 +202,4 @@ nrn_pragma_omp(end declare target)
 #undef y_
 #undef b_
 
-}  // namespace crout
-}  // namespace nmodl
+}  // namespace nmodl::crout
diff --git a/src/solver/newton/newton.hpp b/src/solver/newton/newton.hpp
index 973b4cd332..0da5e7eec0 100644
--- a/src/solver/newton/newton.hpp
+++ b/src/solver/newton/newton.hpp
@@ -20,9 +20,7 @@
 #include <Eigen/Dense>
 #include <Eigen/LU>
 
-namespace nmodl {
-/// newton solver implementations
-namespace newton {
+namespace nmodl::newton {
 
 /**
  * @defgroup solver Solver Implementation
@@ -237,5 +235,4 @@ EIGEN_DEVICE_FUNC int newton_solver(Eigen::Matrix<double, 4, 1>& X,
 
 /** @} */  // end of solver
 
-}  // namespace newton
-}  // namespace nmodl
+}  // namespace nmodl::newton
diff --git a/src/symtab/decl.hpp b/src/symtab/decl.hpp
index 119ebf0f89..d287951600 100644
--- a/src/symtab/decl.hpp
+++ b/src/symtab/decl.hpp
@@ -10,11 +10,9 @@
 /// \file
 /// \brief Forward declarations of symbols in namespace nmodl::symtab
 
-namespace nmodl {
-namespace symtab {
+namespace nmodl::symtab {
 
 class Symbol;
 class SymbolTable;
 
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab
diff --git a/src/symtab/symbol.cpp b/src/symtab/symbol.cpp
index c7fe26744f..5bf47b0e03 100644
--- a/src/symtab/symbol.cpp
+++ b/src/symtab/symbol.cpp
@@ -9,8 +9,7 @@
 #include "utils/logger.hpp"
 #include <ast/ast.hpp>
 
-namespace nmodl {
-namespace symtab {
+namespace nmodl::symtab {
 
 using syminfo::NmodlType;
 using syminfo::Status;
@@ -63,5 +62,4 @@ std::vector<ast::Ast*> Symbol::get_nodes_by_type(
     return _nodes;
 }
 
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab
diff --git a/src/symtab/symbol_properties.cpp b/src/symtab/symbol_properties.cpp
index 8782332ee2..fa0b0d3ded 100644
--- a/src/symtab/symbol_properties.cpp
+++ b/src/symtab/symbol_properties.cpp
@@ -12,9 +12,7 @@
 #include "utils/string_utils.hpp"
 
 
-namespace nmodl {
-namespace symtab {
-namespace syminfo {
+namespace nmodl::symtab::syminfo {
 
 
 // NOLINTNEXTLINE(readability-function-cognitive-complexity)
@@ -206,6 +204,4 @@ std::ostream& operator<<(std::ostream& os, const Status& obj) {
     return os << to_string(obj);
 }
 
-}  // namespace syminfo
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab::syminfo
diff --git a/src/symtab/symbol_properties.hpp b/src/symtab/symbol_properties.hpp
index dad35d8b60..e5b29a7c9d 100644
--- a/src/symtab/symbol_properties.hpp
+++ b/src/symtab/symbol_properties.hpp
@@ -17,11 +17,7 @@
 #include "utils/string_utils.hpp"
 
 
-namespace nmodl {
-namespace symtab {
-
-/// %Symbol information
-namespace syminfo {
+namespace nmodl::symtab::syminfo {
 
 /// \todo Error with pybind if std::underlying_typ is used
 using enum_type = long long;
@@ -285,6 +281,4 @@ std::string to_string(const T& obj) {
     return text;
 }
 
-}  // namespace syminfo
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab::syminfo
diff --git a/src/symtab/symbol_table.cpp b/src/symtab/symbol_table.cpp
index 638141f082..20c5b8ce53 100644
--- a/src/symtab/symbol_table.cpp
+++ b/src/symtab/symbol_table.cpp
@@ -13,8 +13,7 @@
 #include "utils/logger.hpp"
 #include "utils/table_data.hpp"
 
-namespace nmodl {
-namespace symtab {
+namespace nmodl::symtab {
 
 using namespace ast;
 using syminfo::NmodlType;
@@ -527,5 +526,4 @@ void SymbolTable::print(std::ostream& ss, int level) const {
     }
 }
 
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab
diff --git a/src/symtab/symbol_table.hpp b/src/symtab/symbol_table.hpp
index 9b64157f8a..dc2794bebb 100644
--- a/src/symtab/symbol_table.hpp
+++ b/src/symtab/symbol_table.hpp
@@ -21,8 +21,7 @@
 
 #include "symtab/symbol.hpp"
 
-namespace nmodl {
-namespace symtab {
+namespace nmodl::symtab {
 
 
 /**
@@ -294,5 +293,4 @@ class ModelSymbolTable {
 
 /** @} */  // end of sym_tab
 
-}  // namespace symtab
-}  // namespace nmodl
+}  // namespace nmodl::symtab
diff --git a/src/units/units.cpp b/src/units/units.cpp
index 5f1465ab23..ed93a070a9 100644
--- a/src/units/units.cpp
+++ b/src/units/units.cpp
@@ -24,8 +24,7 @@
  * \brief Units processing while being processed from lexer and parser
  */
 
-namespace nmodl {
-namespace units {
+namespace nmodl::units {
 
 Prefix::Prefix(std::string name, const std::string& factor) {
     if (name.back() == '-') {
@@ -330,5 +329,4 @@ void UnitTable::print_base_units(std::ostream& base_units_details) const {
     base_units_details << '\n';
 }
 
-}  // namespace units
-}  // namespace nmodl
+}  // namespace nmodl::units
diff --git a/src/units/units.hpp b/src/units/units.hpp
index 6c770bde79..7e78aad3b3 100644
--- a/src/units/units.hpp
+++ b/src/units/units.hpp
@@ -27,10 +27,8 @@
 #include <utility>
 #include <vector>
 
-
-namespace nmodl {
 /// encapsulates unit database and tables implementation
-namespace units {
+namespace nmodl::units {
 
 /**
  * @defgroup units Unit Implementation
@@ -292,5 +290,4 @@ class UnitTable {
 
 /** @} */  // end of units
 
-}  // namespace units
-}  // namespace nmodl
+}  // namespace nmodl::units
diff --git a/src/utils/common_utils.cpp b/src/utils/common_utils.cpp
index 9bcdeeb8f5..7d16827d35 100644
--- a/src/utils/common_utils.cpp
+++ b/src/utils/common_utils.cpp
@@ -22,8 +22,7 @@
 #define IS_WINDOWS
 #endif
 
-namespace nmodl {
-namespace utils {
+namespace nmodl::utils {
 
 std::string generate_random_string(const int len, UseNumbersInString use_numbers) {
     std::string s(len, 0);
@@ -43,5 +42,4 @@ std::string generate_random_string(const int len, UseNumbersInString use_numbers
     return s;
 }
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/utils/common_utils.hpp b/src/utils/common_utils.hpp
index 2508990917..be0eba7ede 100644
--- a/src/utils/common_utils.hpp
+++ b/src/utils/common_utils.hpp
@@ -24,9 +24,8 @@
  * \brief Common utility functions for file/dir manipulation
  */
 
-namespace nmodl {
 /// file/string manipulation functions
-namespace utils {
+namespace nmodl::utils {
 
 /**
  * @defgroup utils Utility Implementation
@@ -130,5 +129,4 @@ class SingletonRandomString {
 
 /** @} */  // end of utils
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/utils/perf_stat.cpp b/src/utils/perf_stat.cpp
index 6156249ea7..ae3b4de051 100644
--- a/src/utils/perf_stat.cpp
+++ b/src/utils/perf_stat.cpp
@@ -12,8 +12,7 @@
 #include "utils/perf_stat.hpp"
 #include "utils/table_data.hpp"
 
-namespace nmodl {
-namespace utils {
+namespace nmodl::utils {
 
 PerfStat operator+(const PerfStat& first, const PerfStat& second) {
     PerfStat result;
@@ -115,5 +114,4 @@ std::vector<std::string> PerfStat::values() const {
     return row;
 }
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/utils/perf_stat.hpp b/src/utils/perf_stat.hpp
index bcb76de474..c273afb12d 100644
--- a/src/utils/perf_stat.hpp
+++ b/src/utils/perf_stat.hpp
@@ -16,8 +16,7 @@
 #include <string>
 #include <vector>
 
-namespace nmodl {
-namespace utils {
+namespace nmodl::utils {
 
 /**
  * @addtogroup utils
@@ -108,5 +107,4 @@ struct PerfStat {
 
 /** @} */  // end of utils
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/utils/string_utils.cpp b/src/utils/string_utils.cpp
index 76a7c12506..dd60f75e91 100644
--- a/src/utils/string_utils.cpp
+++ b/src/utils/string_utils.cpp
@@ -12,8 +12,7 @@
 #include <limits>
 #include <string>
 
-namespace nmodl {
-namespace stringutils {
+namespace nmodl::stringutils {
 
 std::string to_string(double value, const std::string& format_spec) {
     // double containing integer value
@@ -27,5 +26,4 @@ std::string to_string(double value, const std::string& format_spec) {
     return fmt::format(format_spec, value);
 }
 
-}  // namespace stringutils
-}  // namespace nmodl
+}  // namespace nmodl::stringutils
diff --git a/src/utils/string_utils.hpp b/src/utils/string_utils.hpp
index 749ee84c0f..a0176ec708 100644
--- a/src/utils/string_utils.hpp
+++ b/src/utils/string_utils.hpp
@@ -22,9 +22,8 @@
 #include <sstream>
 #include <vector>
 
-namespace nmodl {
 /// string utility functions
-namespace stringutils {
+namespace nmodl::stringutils {
 
 /**
  * \addtogroup utils
@@ -182,5 +181,4 @@ std::string to_string(double value, const std::string& format_spec = "{:.16g}");
 
 /** \} */  // end of utils
 
-}  // namespace stringutils
-}  // namespace nmodl
+}  // namespace nmodl::stringutils
diff --git a/src/utils/table_data.cpp b/src/utils/table_data.cpp
index fd6c3b56a2..a6c17ca5f6 100644
--- a/src/utils/table_data.cpp
+++ b/src/utils/table_data.cpp
@@ -12,8 +12,7 @@
 #include "utils/string_utils.hpp"
 #include "utils/table_data.hpp"
 
-namespace nmodl {
-namespace utils {
+namespace nmodl::utils {
 
 /**
  *   Print table data in below shown format: title as first row (centrally aligned),
@@ -128,5 +127,4 @@ void TableData::print(int indent) const {
     print(std::cout, indent);
 }
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/utils/table_data.hpp b/src/utils/table_data.hpp
index 7129a8c974..0f8adf35ed 100644
--- a/src/utils/table_data.hpp
+++ b/src/utils/table_data.hpp
@@ -18,8 +18,7 @@
 #include "utils/string_utils.hpp"
 
 
-namespace nmodl {
-namespace utils {
+namespace nmodl::utils {
 
 /**
  * @addtogroup utils
@@ -55,5 +54,4 @@ struct TableData {
 
 /** @} */  // end of utils
 
-}  // namespace utils
-}  // namespace nmodl
+}  // namespace nmodl::utils
diff --git a/src/visitors/after_cvode_to_cnexp_visitor.cpp b/src/visitors/after_cvode_to_cnexp_visitor.cpp
index 13caa477ef..563bfa326c 100644
--- a/src/visitors/after_cvode_to_cnexp_visitor.cpp
+++ b/src/visitors/after_cvode_to_cnexp_visitor.cpp
@@ -13,8 +13,7 @@
 #include "codegen/codegen_naming.hpp"
 #include "utils/logger.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void AfterCVodeToCnexpVisitor::visit_solve_block(ast::SolveBlock& node) {
     const auto& method = node.get_method();
@@ -27,5 +26,4 @@ void AfterCVodeToCnexpVisitor::visit_solve_block(ast::SolveBlock& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/after_cvode_to_cnexp_visitor.hpp b/src/visitors/after_cvode_to_cnexp_visitor.hpp
index 182a01fb8b..33fdaad289 100644
--- a/src/visitors/after_cvode_to_cnexp_visitor.hpp
+++ b/src/visitors/after_cvode_to_cnexp_visitor.hpp
@@ -19,8 +19,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -50,5 +49,4 @@ class AfterCVodeToCnexpVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/constant_folder_visitor.cpp b/src/visitors/constant_folder_visitor.cpp
index 69fab6bf25..970bf78cc2 100644
--- a/src/visitors/constant_folder_visitor.cpp
+++ b/src/visitors/constant_folder_visitor.cpp
@@ -12,8 +12,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /// check if given expression is a number
 /// note that the DEFINE node is already expanded to integer
@@ -177,5 +176,4 @@ void ConstantFolderVisitor::visit_wrapped_expression(ast::WrappedExpression& nod
     logger->debug("ConstantFolderVisitor : expression {} folded to {}", nmodl_before, nmodl_after);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/constant_folder_visitor.hpp b/src/visitors/constant_folder_visitor.hpp
index 6c9e735c53..2b97ffd0e5 100644
--- a/src/visitors/constant_folder_visitor.hpp
+++ b/src/visitors/constant_folder_visitor.hpp
@@ -22,8 +22,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -59,5 +58,4 @@ class ConstantFolderVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/defuse_analyze_visitor.cpp b/src/visitors/defuse_analyze_visitor.cpp
index 7388d090de..66c0de2e04 100644
--- a/src/visitors/defuse_analyze_visitor.cpp
+++ b/src/visitors/defuse_analyze_visitor.cpp
@@ -13,8 +13,7 @@
 #include "ast/all.hpp"
 #include "utils/logger.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using printer::JSONPrinter;
 using symtab::syminfo::NmodlType;
@@ -444,5 +443,4 @@ DUChain DefUseAnalyzeVisitor::analyze(const ast::Ast& node, const std::string& n
     return usage;
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/defuse_analyze_visitor.hpp b/src/visitors/defuse_analyze_visitor.hpp
index a36ac9e2f3..bf2eec918f 100644
--- a/src/visitors/defuse_analyze_visitor.hpp
+++ b/src/visitors/defuse_analyze_visitor.hpp
@@ -21,8 +21,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /// Represent a state in Def-Use chain
 enum class DUState {
@@ -312,5 +311,4 @@ class DefUseAnalyzeVisitor: protected ConstAstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/global_var_visitor.cpp b/src/visitors/global_var_visitor.cpp
index ae84720597..9b57c91647 100644
--- a/src/visitors/global_var_visitor.cpp
+++ b/src/visitors/global_var_visitor.cpp
@@ -17,8 +17,7 @@
 #include "visitors/global_var_visitor.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void GlobalToRangeVisitor::visit_neuron_block(ast::NeuronBlock& node) {
     ast::RangeVarVector range_variables;
@@ -65,5 +64,4 @@ void GlobalToRangeVisitor::visit_neuron_block(ast::NeuronBlock& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/global_var_visitor.hpp b/src/visitors/global_var_visitor.hpp
index 8cecb5e4ce..73eebd793a 100644
--- a/src/visitors/global_var_visitor.hpp
+++ b/src/visitors/global_var_visitor.hpp
@@ -19,8 +19,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -87,5 +86,4 @@ class GlobalToRangeVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/implicit_argument_visitor.cpp b/src/visitors/implicit_argument_visitor.cpp
index 14d84c1299..8fdc69330e 100644
--- a/src/visitors/implicit_argument_visitor.cpp
+++ b/src/visitors/implicit_argument_visitor.cpp
@@ -12,8 +12,7 @@
 #include "codegen/codegen_naming.hpp"
 #include "lexer/token_mapping.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void ImplicitArgumentVisitor::visit_function_call(ast::FunctionCall& node) {
     auto function_name = node.get_node_name();
@@ -53,5 +52,4 @@ void ImplicitArgumentVisitor::visit_function_call(ast::FunctionCall& node) {
     node.visit_children(*this);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/implicit_argument_visitor.hpp b/src/visitors/implicit_argument_visitor.hpp
index effca8793c..63be545cac 100644
--- a/src/visitors/implicit_argument_visitor.hpp
+++ b/src/visitors/implicit_argument_visitor.hpp
@@ -15,8 +15,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -38,5 +37,4 @@ struct ImplicitArgumentVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/indexedname_visitor.cpp b/src/visitors/indexedname_visitor.cpp
index c039c52558..044d7fbf15 100644
--- a/src/visitors/indexedname_visitor.cpp
+++ b/src/visitors/indexedname_visitor.cpp
@@ -9,8 +9,7 @@
 #include "ast/binary_expression.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void IndexedNameVisitor::visit_indexed_name(ast::IndexedName& node) {
     indexed_name = nmodl::get_indexed_name(node);
@@ -34,5 +33,4 @@ std::string IndexedNameVisitor::get_indexed_name() {
     return indexed_name;
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/indexedname_visitor.hpp b/src/visitors/indexedname_visitor.hpp
index 9d38b6db33..81e2134fcb 100644
--- a/src/visitors/indexedname_visitor.hpp
+++ b/src/visitors/indexedname_visitor.hpp
@@ -20,8 +20,7 @@
 #include "ast/program.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -64,5 +63,4 @@ class IndexedNameVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/inline_visitor.cpp b/src/visitors/inline_visitor.cpp
index 5820ddd2a4..81563a645e 100644
--- a/src/visitors/inline_visitor.cpp
+++ b/src/visitors/inline_visitor.cpp
@@ -16,8 +16,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using namespace ast;
 
@@ -326,5 +325,4 @@ void InlineVisitor::visit_program(Program& node) {
     node.visit_children(*this);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/inline_visitor.hpp b/src/visitors/inline_visitor.hpp
index 9a728da04b..84659c1a26 100644
--- a/src/visitors/inline_visitor.hpp
+++ b/src/visitors/inline_visitor.hpp
@@ -18,8 +18,7 @@
 #include "symtab/decl.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -198,5 +197,4 @@ class InlineVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/kinetic_block_visitor.cpp b/src/visitors/kinetic_block_visitor.cpp
index 69a317a3b3..4fd2ac0a9f 100644
--- a/src/visitors/kinetic_block_visitor.cpp
+++ b/src/visitors/kinetic_block_visitor.cpp
@@ -14,8 +14,7 @@
 #include "visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using symtab::syminfo::NmodlType;
 
@@ -489,5 +488,4 @@ void KineticBlockVisitor::visit_program(ast::Program& node) {
     node.set_blocks(std::move(blocks));
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/kinetic_block_visitor.hpp b/src/visitors/kinetic_block_visitor.hpp
index 0f67260594..9ae057aef0 100644
--- a/src/visitors/kinetic_block_visitor.hpp
+++ b/src/visitors/kinetic_block_visitor.hpp
@@ -20,8 +20,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -151,5 +150,4 @@ class KineticBlockVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/local_to_assigned_visitor.cpp b/src/visitors/local_to_assigned_visitor.cpp
index 89f7734899..00e87b975a 100644
--- a/src/visitors/local_to_assigned_visitor.cpp
+++ b/src/visitors/local_to_assigned_visitor.cpp
@@ -15,8 +15,7 @@
 #include "visitors/local_to_assigned_visitor.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void LocalToAssignedVisitor::visit_program(ast::Program& node) {
     ast::AssignedDefinitionVector assigned_variables;
@@ -81,5 +80,4 @@ void LocalToAssignedVisitor::visit_program(ast::Program& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/local_to_assigned_visitor.hpp b/src/visitors/local_to_assigned_visitor.hpp
index 4e757718ef..b68b592300 100644
--- a/src/visitors/local_to_assigned_visitor.hpp
+++ b/src/visitors/local_to_assigned_visitor.hpp
@@ -14,8 +14,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -79,5 +78,4 @@ class LocalToAssignedVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/local_var_rename_visitor.cpp b/src/visitors/local_var_rename_visitor.cpp
index a93a1128a6..1e9322a843 100644
--- a/src/visitors/local_var_rename_visitor.cpp
+++ b/src/visitors/local_var_rename_visitor.cpp
@@ -14,8 +14,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using symtab::SymbolTable;
 
@@ -75,5 +74,4 @@ void LocalVarRenameVisitor::visit_statement_block(ast::StatementBlock& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/local_var_rename_visitor.hpp b/src/visitors/local_var_rename_visitor.hpp
index a73196e194..2af0c67d91 100644
--- a/src/visitors/local_var_rename_visitor.hpp
+++ b/src/visitors/local_var_rename_visitor.hpp
@@ -18,8 +18,7 @@
 #include "symtab/decl.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -77,5 +76,4 @@ class LocalVarRenameVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/localize_visitor.cpp b/src/visitors/localize_visitor.cpp
index 0181940b57..071aebe4fb 100644
--- a/src/visitors/localize_visitor.cpp
+++ b/src/visitors/localize_visitor.cpp
@@ -14,8 +14,7 @@
 #include "utils/logger.hpp"
 #include "visitors/defuse_analyze_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using symtab::Symbol;
 using symtab::syminfo::NmodlType;
@@ -159,5 +158,4 @@ void LocalizeVisitor::visit_program(const ast::Program& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/localize_visitor.hpp b/src/visitors/localize_visitor.hpp
index 821e072fe2..577f3580c2 100644
--- a/src/visitors/localize_visitor.hpp
+++ b/src/visitors/localize_visitor.hpp
@@ -18,8 +18,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -104,5 +103,4 @@ class LocalizeVisitor: public ConstAstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/loop_unroll_visitor.cpp b/src/visitors/loop_unroll_visitor.cpp
index 35697f19be..f93d681733 100644
--- a/src/visitors/loop_unroll_visitor.cpp
+++ b/src/visitors/loop_unroll_visitor.cpp
@@ -13,8 +13,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \class IndexRemover
@@ -130,7 +129,7 @@ static std::shared_ptr<ast::ExpressionStatement> unroll_for_loop(
     }
 
     /// create new statement representing unrolled loop
-    auto block = new ast::StatementBlock(std::move(statements));
+    auto block = std::make_shared<ast::StatementBlock>(statements);
     return std::make_shared<ast::ExpressionStatement>(block);
 }
 
@@ -167,5 +166,4 @@ void LoopUnrollVisitor::visit_statement_block(ast::StatementBlock& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/loop_unroll_visitor.hpp b/src/visitors/loop_unroll_visitor.hpp
index 054dfb89b9..9d2f464a6e 100644
--- a/src/visitors/loop_unroll_visitor.hpp
+++ b/src/visitors/loop_unroll_visitor.hpp
@@ -16,8 +16,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -65,5 +64,4 @@ class LoopUnrollVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/neuron_solve_visitor.cpp b/src/visitors/neuron_solve_visitor.cpp
index d8da1e03c2..435e19bbe6 100644
--- a/src/visitors/neuron_solve_visitor.cpp
+++ b/src/visitors/neuron_solve_visitor.cpp
@@ -15,8 +15,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void NeuronSolveVisitor::visit_solve_block(ast::SolveBlock& node) {
     auto name = node.get_block_name()->get_node_name();
@@ -115,5 +114,4 @@ void NeuronSolveVisitor::visit_program(ast::Program& node) {
     node.visit_children(*this);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/neuron_solve_visitor.hpp b/src/visitors/neuron_solve_visitor.hpp
index 85029ed43e..e1b14b3c37 100644
--- a/src/visitors/neuron_solve_visitor.hpp
+++ b/src/visitors/neuron_solve_visitor.hpp
@@ -19,8 +19,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup solver
@@ -73,5 +72,4 @@ class NeuronSolveVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/perf_visitor.cpp b/src/visitors/perf_visitor.cpp
index 078c8300e0..216518d699 100644
--- a/src/visitors/perf_visitor.cpp
+++ b/src/visitors/perf_visitor.cpp
@@ -13,8 +13,7 @@
 #include "printer/json_printer.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using printer::JSONPrinter;
 using symtab::Symbol;
@@ -577,5 +576,4 @@ void PerfVisitor::update_memory_ops(const std::string& name) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/perf_visitor.hpp b/src/visitors/perf_visitor.hpp
index 7fa0c01d3f..8b44318151 100644
--- a/src/visitors/perf_visitor.hpp
+++ b/src/visitors/perf_visitor.hpp
@@ -22,8 +22,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -253,5 +252,4 @@ class PerfVisitor: public ConstAstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/rename_visitor.cpp b/src/visitors/rename_visitor.cpp
index 0328d01417..4e1857f825 100644
--- a/src/visitors/rename_visitor.cpp
+++ b/src/visitors/rename_visitor.cpp
@@ -13,8 +13,7 @@
 #include "visitors/visitor_utils.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 
 std::string RenameVisitor::new_name_generator(const std::string& old_name) {
@@ -101,5 +100,4 @@ void RenameVisitor::visit_verbatim(const ast::Verbatim& node) {
     statement->set(result.str());
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/rename_visitor.hpp b/src/visitors/rename_visitor.hpp
index 3bd62fb016..bb8fcdf14d 100644
--- a/src/visitors/rename_visitor.hpp
+++ b/src/visitors/rename_visitor.hpp
@@ -19,8 +19,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -110,5 +109,4 @@ class RenameVisitor: public ConstAstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/semantic_analysis_visitor.cpp b/src/visitors/semantic_analysis_visitor.cpp
index 40d6b1667b..571ec4ef59 100644
--- a/src/visitors/semantic_analysis_visitor.cpp
+++ b/src/visitors/semantic_analysis_visitor.cpp
@@ -18,8 +18,7 @@
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 bool SemanticAnalysisVisitor::check(const ast::Program& node) {
     check_fail = false;
@@ -170,5 +169,4 @@ void SemanticAnalysisVisitor::visit_mutex_unlock(const ast::MutexUnlock& /* node
     /// -->
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/semantic_analysis_visitor.hpp b/src/visitors/semantic_analysis_visitor.hpp
index 1deffcb154..4c43e10ba1 100644
--- a/src/visitors/semantic_analysis_visitor.hpp
+++ b/src/visitors/semantic_analysis_visitor.hpp
@@ -35,8 +35,7 @@
 #include "ast/ast.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 class SemanticAnalysisVisitor: public ConstAstVisitor {
   private:
@@ -90,5 +89,4 @@ class SemanticAnalysisVisitor: public ConstAstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/solve_block_visitor.cpp b/src/visitors/solve_block_visitor.cpp
index 7355789ad4..2a1d0f71a6 100644
--- a/src/visitors/solve_block_visitor.cpp
+++ b/src/visitors/solve_block_visitor.cpp
@@ -14,8 +14,7 @@
 #include "codegen/codegen_naming.hpp"
 #include "visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void SolveBlockVisitor::visit_breakpoint_block(ast::BreakpointBlock& node) {
     in_breakpoint_block = true;
@@ -93,5 +92,4 @@ void SolveBlockVisitor::visit_program(ast::Program& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/solve_block_visitor.hpp b/src/visitors/solve_block_visitor.hpp
index a22509d130..e10763b53b 100644
--- a/src/visitors/solve_block_visitor.hpp
+++ b/src/visitors/solve_block_visitor.hpp
@@ -15,8 +15,7 @@
 #include "symtab/decl.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -52,5 +51,4 @@ class SolveBlockVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/steadystate_visitor.cpp b/src/visitors/steadystate_visitor.cpp
index 4c69600d1f..c2b426ebf8 100644
--- a/src/visitors/steadystate_visitor.cpp
+++ b/src/visitors/steadystate_visitor.cpp
@@ -12,8 +12,7 @@
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 std::shared_ptr<ast::DerivativeBlock> SteadystateVisitor::create_steadystate_block(
     const std::shared_ptr<ast::SolveBlock>& solve_block,
@@ -105,5 +104,4 @@ void SteadystateVisitor::visit_program(ast::Program& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/steadystate_visitor.hpp b/src/visitors/steadystate_visitor.hpp
index 6b4e3432ad..55ffc28ef6 100644
--- a/src/visitors/steadystate_visitor.hpp
+++ b/src/visitors/steadystate_visitor.hpp
@@ -14,8 +14,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -69,5 +68,4 @@ class SteadystateVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_conductance_visitor.cpp b/src/visitors/sympy_conductance_visitor.cpp
index 30aa9bfd4e..593a2edfc5 100644
--- a/src/visitors/sympy_conductance_visitor.cpp
+++ b/src/visitors/sympy_conductance_visitor.cpp
@@ -17,8 +17,7 @@
 
 namespace pywrap = nmodl::pybind_wrappers;
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using ast::AstNodeType;
 using ast::BinaryOp;
@@ -244,5 +243,4 @@ void SympyConductanceVisitor::visit_program(ast::Program& node) {
     node.visit_children(*this);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_conductance_visitor.hpp b/src/visitors/sympy_conductance_visitor.hpp
index cb76bdf2fd..e891f87d85 100644
--- a/src/visitors/sympy_conductance_visitor.hpp
+++ b/src/visitors/sympy_conductance_visitor.hpp
@@ -18,9 +18,7 @@
 
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -101,5 +99,4 @@ class SympyConductanceVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_replace_solutions_visitor.cpp b/src/visitors/sympy_replace_solutions_visitor.cpp
index 9906c5577e..5aaf9dcc13 100644
--- a/src/visitors/sympy_replace_solutions_visitor.cpp
+++ b/src/visitors/sympy_replace_solutions_visitor.cpp
@@ -12,8 +12,7 @@
 #include "utils/logger.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \details SympyReplaceSolutionsVisitor tells us that a new equation appear and, depending where
@@ -462,5 +461,4 @@ void SympyReplaceSolutionsVisitor::StatementDispenser::tag_all_statements() {
 }
 
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_replace_solutions_visitor.hpp b/src/visitors/sympy_replace_solutions_visitor.hpp
index 42bc4da2d0..d3b7e95983 100644
--- a/src/visitors/sympy_replace_solutions_visitor.hpp
+++ b/src/visitors/sympy_replace_solutions_visitor.hpp
@@ -21,8 +21,7 @@
 #include <unordered_set>
 #include <vector>
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -498,5 +497,4 @@ class SympyReplaceSolutionsVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_solver_visitor.cpp b/src/visitors/sympy_solver_visitor.cpp
index 040bddbc69..061b8d7819 100644
--- a/src/visitors/sympy_solver_visitor.cpp
+++ b/src/visitors/sympy_solver_visitor.cpp
@@ -19,8 +19,7 @@
 
 namespace pywrap = nmodl::pybind_wrappers;
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using symtab::syminfo::NmodlType;
 
@@ -682,5 +681,4 @@ void SympySolverVisitor::visit_program(ast::Program& node) {
     node.visit_children(*this);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/sympy_solver_visitor.hpp b/src/visitors/sympy_solver_visitor.hpp
index b5a5b13516..4033d86174 100644
--- a/src/visitors/sympy_solver_visitor.hpp
+++ b/src/visitors/sympy_solver_visitor.hpp
@@ -23,8 +23,7 @@
 #include "visitors/ast_visitor.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -187,5 +186,4 @@ class SympySolverVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/symtab_visitor_helper.hpp b/src/visitors/symtab_visitor_helper.hpp
index cfe299d64e..5298889477 100644
--- a/src/visitors/symtab_visitor_helper.hpp
+++ b/src/visitors/symtab_visitor_helper.hpp
@@ -15,8 +15,7 @@
 #include "visitors/symtab_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 using symtab::Symbol;
 using symtab::syminfo::NmodlType;
@@ -261,5 +260,4 @@ void SymtabVisitor::visit_table_statement(ast::TableStatement& node) {
     update_symbol(node.get_depend_vars(), NmodlType::table_assigned_var, num_values);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/units_visitor.cpp b/src/visitors/units_visitor.cpp
index 2ad612d0ea..ca09641751 100644
--- a/src/visitors/units_visitor.cpp
+++ b/src/visitors/units_visitor.cpp
@@ -16,8 +16,7 @@
  * by the Units Parser used to parse the \c nrnunits.lib file
  */
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void UnitsVisitor::visit_program(ast::Program& node) {
     units_driver.parse_file(units_dir);
@@ -134,5 +133,4 @@ void UnitsVisitor::visit_factor_def(ast::FactorDef& node) {
     }
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/units_visitor.hpp b/src/visitors/units_visitor.hpp
index 543b0655a0..a987ca1c47 100644
--- a/src/visitors/units_visitor.hpp
+++ b/src/visitors/units_visitor.hpp
@@ -20,8 +20,7 @@
 #include "visitors/ast_visitor.hpp"
 #include "visitors/visitor_utils.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -87,5 +86,4 @@ class UnitsVisitor: public AstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/var_usage_visitor.cpp b/src/visitors/var_usage_visitor.cpp
index 5f355400da..932e756cc8 100644
--- a/src/visitors/var_usage_visitor.cpp
+++ b/src/visitors/var_usage_visitor.cpp
@@ -12,8 +12,7 @@
 #include "ast/name.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /// rename matching variable
 void VarUsageVisitor::visit_name(const ast::Name& node) {
@@ -30,5 +29,4 @@ bool VarUsageVisitor::variable_used(const ast::Node& node, std::string name) {
     return used;
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/var_usage_visitor.hpp b/src/visitors/var_usage_visitor.hpp
index 933f3b5f0f..0ceca7d5ca 100644
--- a/src/visitors/var_usage_visitor.hpp
+++ b/src/visitors/var_usage_visitor.hpp
@@ -17,8 +17,7 @@
 #include "visitors/ast_visitor.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * \addtogroup visitor_classes
@@ -48,5 +47,4 @@ class VarUsageVisitor: protected ConstAstVisitor {
 
 /** \} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/verbatim_var_rename_visitor.cpp b/src/visitors/verbatim_var_rename_visitor.cpp
index 3908a88679..49e3f923b3 100644
--- a/src/visitors/verbatim_var_rename_visitor.cpp
+++ b/src/visitors/verbatim_var_rename_visitor.cpp
@@ -14,8 +14,7 @@
 #include "src/utils/logger.hpp"
 
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void VerbatimVarRenameVisitor::visit_statement_block(ast::StatementBlock& node) {
     if (node.get_statements().empty()) {
@@ -93,5 +92,4 @@ void VerbatimVarRenameVisitor::visit_verbatim(ast::Verbatim& node) {
     statement->set(oss.str());
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/verbatim_var_rename_visitor.hpp b/src/visitors/verbatim_var_rename_visitor.hpp
index 81baddb3fd..0077c44542 100644
--- a/src/visitors/verbatim_var_rename_visitor.hpp
+++ b/src/visitors/verbatim_var_rename_visitor.hpp
@@ -18,8 +18,7 @@
 #include "symtab/symbol_table.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -72,5 +71,4 @@ class VerbatimVarRenameVisitor: public AstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/verbatim_visitor.cpp b/src/visitors/verbatim_visitor.cpp
index a9c540b15f..da186ef46d 100644
--- a/src/visitors/verbatim_visitor.cpp
+++ b/src/visitors/verbatim_visitor.cpp
@@ -12,8 +12,7 @@
 #include "ast/string.hpp"
 #include "ast/verbatim.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 void VerbatimVisitor::visit_verbatim(const ast::Verbatim& node) {
     std::string block;
@@ -28,5 +27,4 @@ void VerbatimVisitor::visit_verbatim(const ast::Verbatim& node) {
     blocks.push_back(block);
 }
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/src/visitors/verbatim_visitor.hpp b/src/visitors/verbatim_visitor.hpp
index d17c06b5dd..180322366a 100644
--- a/src/visitors/verbatim_visitor.hpp
+++ b/src/visitors/verbatim_visitor.hpp
@@ -17,8 +17,7 @@
 #include "ast/ast.hpp"
 #include "visitors/ast_visitor.hpp"
 
-namespace nmodl {
-namespace visitor {
+namespace nmodl::visitor {
 
 /**
  * @addtogroup visitor_classes
@@ -59,5 +58,4 @@ class VerbatimVisitor: public ConstAstVisitor {
 
 /** @} */  // end of visitor_classes
 
-}  // namespace visitor
-}  // namespace nmodl
+}  // namespace nmodl::visitor
diff --git a/test/unit/codegen/codegen_compatibility_visitor.cpp b/test/unit/codegen/codegen_compatibility_visitor.cpp
index 5e686498f0..141f4a1ae0 100644
--- a/test/unit/codegen/codegen_compatibility_visitor.cpp
+++ b/test/unit/codegen/codegen_compatibility_visitor.cpp
@@ -8,7 +8,6 @@
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers_string.hpp>
 
-#include "ast/program.hpp"
 #include "codegen/codegen_compatibility_visitor.hpp"
 #include "parser/nmodl_driver.hpp"
 #include "test/unit/utils/test_utils.hpp"
@@ -31,7 +30,7 @@ bool runCompatibilityVisitor(const std::string& nmodl_text) {
     return CodegenCompatibilityVisitor().find_unhandled_ast_nodes(*ast);
 }
 
-SCENARIO("Uncompatible constructs should failed", "[codegen][compatibility_visitor]") {
+SCENARIO("Incompatible constructs should failed", "[codegen][compatibility_visitor]") {
     GIVEN("A mod file containing an EXTERNAL construct") {
         std::string const nmodl_text = R"(
             NEURON {
diff --git a/test/unit/codegen/codegen_cpp_visitor.cpp b/test/unit/codegen/codegen_cpp_visitor.cpp
index 967c5d3267..fae23c26c4 100644
--- a/test/unit/codegen/codegen_cpp_visitor.cpp
+++ b/test/unit/codegen/codegen_cpp_visitor.cpp
@@ -11,7 +11,6 @@
 #include "ast/program.hpp"
 #include "codegen/codegen_acc_visitor.hpp"
 #include "codegen/codegen_cpp_visitor.hpp"
-#include "codegen/codegen_helper_visitor.hpp"
 #include "parser/nmodl_driver.hpp"
 #include "test/unit/utils/test_utils.hpp"
 #include "visitors/implicit_argument_visitor.hpp"
@@ -299,7 +298,7 @@ SCENARIO("Check instance variable definition order", "[codegen][var_order]") {
     }
 }
 
-std::string get_instance_structure(std::string nmodl_text) {
+std::string get_instance_structure(const std::string& nmodl_text) {
     // parse mod file & print mechanism structure
     auto const ast = NmodlDriver{}.parse_string(nmodl_text);
     // add implicit arguments
@@ -535,8 +534,7 @@ SCENARIO("Check that BEFORE/AFTER block are well generated", "[codegen][before/a
                 inc = inc + 1.0;
             }
         })";
-                auto const expected = generated_code;
-                REQUIRE_THAT(generated, ContainsSubstring(expected));
+                REQUIRE_THAT(generated, ContainsSubstring(generated_code));
             }
             // AFTER SOLVE
             {
@@ -560,8 +558,7 @@ SCENARIO("Check that BEFORE/AFTER block are well generated", "[codegen][before/a
                 }
             }
         })";
-                auto const expected = generated_code;
-                REQUIRE_THAT(generated, ContainsSubstring(expected));
+                REQUIRE_THAT(generated, ContainsSubstring(generated_code));
             }
             // BEFORE INITIAL
             {
@@ -582,8 +579,7 @@ SCENARIO("Check that BEFORE/AFTER block are well generated", "[codegen][before/a
                 inc = 0.0;
             }
         })";
-                auto const expected = generated_code;
-                REQUIRE_THAT(generated, ContainsSubstring(expected));
+                REQUIRE_THAT(generated, ContainsSubstring(generated_code));
             }
             // AFTER INITIAL
             {
@@ -604,8 +600,7 @@ SCENARIO("Check that BEFORE/AFTER block are well generated", "[codegen][before/a
                 inc = 0.0;
             }
         })";
-                auto const expected = generated_code;
-                REQUIRE_THAT(generated, ContainsSubstring(expected));
+                REQUIRE_THAT(generated, ContainsSubstring(generated_code));
             }
             // BEFORE STEP
             {
@@ -626,8 +621,7 @@ SCENARIO("Check that BEFORE/AFTER block are well generated", "[codegen][before/a
                 inc = 0.0;
             }
         })";
-                auto const expected = generated_code;
-                REQUIRE_THAT(generated, ContainsSubstring(expected));
+                REQUIRE_THAT(generated, ContainsSubstring(generated_code));
             }
         }
     }