constepxr scope guards (#58)

Morwenn · Oct 23, 2022 · c1e1725 · c1e1725
1 parent e513e56
commit c1e1725
Showing 1 changed file with 27 additions and 14 deletions.
diff --git a/include/cpp-sort/detail/scope_exit.h b/include/cpp-sort/detail/scope_exit.h
@@ -14,6 +14,19 @@
 
 namespace cppsort::detail
 {
+    constexpr auto uncaught_exceptions() noexcept
+        -> int
+    {
+        if (std::is_constant_evaluated()) {
+            // Throwing an exception at compile time terminates the
+            // compilation process, so there can never be an exception
+            // in flight in a constant-evaluated expressions
+            return 0;
+        } else {
+            return std::uncaught_exceptions();
+        }
+    }
+
     template<typename EF>
     struct scope_exit
     {
@@ -25,33 +38,33 @@ namespace cppsort::detail
         public:
 
             template<typename EFP>
-            explicit scope_exit(EFP&& func)
+            constexpr explicit scope_exit(EFP&& func)
                 noexcept(std::is_nothrow_constructible_v<EF, EFP> ||
                          std::is_nothrow_constructible_v<EF, EFP&>):
                 exit_function(std::forward<EFP>(func))
             {}
 
-            scope_exit(scope_exit&& rhs)
+            constexpr scope_exit(scope_exit&& rhs)
                 noexcept(std::is_nothrow_move_constructible_v<EF> ||
                          std::is_nothrow_copy_constructible_v<EF>):
                 exit_function(std::forward<EF>(rhs.exit_function))
             {}
 
-            ~scope_exit()
+            constexpr ~scope_exit()
                 noexcept(noexcept(exit_function()))
             {
                 if (execute_on_destruction) {
                     exit_function();
                 }
             }
 
-            auto activate() noexcept
+            constexpr auto activate() noexcept
                 -> void
             {
                 execute_on_destruction = true;
             }
 
-            auto deactivate() noexcept
+            constexpr auto deactivate() noexcept
                 -> void
             {
                 execute_on_destruction = false;
@@ -63,7 +76,7 @@ namespace cppsort::detail
     };
 
     template<typename EF>
-    auto make_scope_exit(EF&& function)
+    constexpr auto make_scope_exit(EF&& function)
         -> scope_exit<EF>
     {
         return scope_exit<EF>(std::forward<EF>(function));
@@ -76,38 +89,38 @@ namespace cppsort::detail
 
             EF exit_function;
             bool execute_on_destruction = true;
-            int uncaught_on_creation = std::uncaught_exceptions();
+            int uncaught_on_creation = uncaught_exceptions();
 
         public:
 
             template<typename EFP>
-            explicit scope_success(EFP&& func)
+            constexpr explicit scope_success(EFP&& func)
                 noexcept(std::is_nothrow_constructible_v<EF, EFP> ||
                          std::is_nothrow_constructible_v<EF, EFP&>):
                 exit_function(std::forward<EFP>(func))
             {}
 
-            scope_success(scope_success&& rhs)
+            constexpr scope_success(scope_success&& rhs)
                 noexcept(std::is_nothrow_move_constructible_v<EF> ||
                          std::is_nothrow_copy_constructible_v<EF>):
                 exit_function(std::forward<EF>(rhs.exit_function))
             {}
 
-            ~scope_success()
+            constexpr ~scope_success()
                 noexcept(noexcept(exit_function()))
             {
-                if (execute_on_destruction && std::uncaught_exceptions() <= uncaught_on_creation) {
+                if (execute_on_destruction && uncaught_exceptions() <= uncaught_on_creation) {
                     exit_function();
                 }
             }
 
-            auto activate() noexcept
+            constexpr auto activate() noexcept
                 -> void
             {
                 execute_on_destruction = true;
             }
 
-            auto deactivate() noexcept
+            constexpr auto deactivate() noexcept
                 -> void
             {
                 execute_on_destruction = false;
@@ -119,7 +132,7 @@ namespace cppsort::detail
     };
 
     template<typename EF>
-    auto make_scope_success(EF&& function)
+    constexpr auto make_scope_success(EF&& function)
         -> scope_success<EF>
     {
         return scope_success<EF>(std::forward<EF>(function));