diff --git a/Gemfile b/Gemfile
index 07879a5..6660944 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 source "https://rubygems.org"
 
 eval_gemfile "Gemfile.devtools"
diff --git a/Guardfile b/Guardfile
index 6a5ea8b..f06eb0f 100644
--- a/Guardfile
+++ b/Guardfile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 guard :rspec, cmd: "bundle exec rspec" do
   watch(%r{^spec/.+_spec\.rb$})
   watch(%r{^spec/(spec_helper|support)}) { "spec" }
diff --git a/Rakefile b/Rakefile
index c6d919b..0e5891d 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "bundler/setup"
 Bundler::GemHelper.install_tasks
 
diff --git a/lib/dry-initializer.rb b/lib/dry-initializer.rb
index 9b17aa8..64e4a2a 100644
--- a/lib/dry-initializer.rb
+++ b/lib/dry-initializer.rb
@@ -1 +1,3 @@
+# frozen_string_literal: true
+
 require_relative "dry/initializer"
diff --git a/lib/dry/initializer.rb b/lib/dry/initializer.rb
index cb7da21..08b49cf 100644
--- a/lib/dry/initializer.rb
+++ b/lib/dry/initializer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "set"
 
 # Namespace for gems in a dry-rb community
diff --git a/lib/dry/initializer/builders.rb b/lib/dry/initializer/builders.rb
index 77ba303..c9218f7 100644
--- a/lib/dry/initializer/builders.rb
+++ b/lib/dry/initializer/builders.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     # @private
diff --git a/lib/dry/initializer/builders/attribute.rb b/lib/dry/initializer/builders/attribute.rb
index b49227f..1e6f643 100644
--- a/lib/dry/initializer/builders/attribute.rb
+++ b/lib/dry/initializer/builders/attribute.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Builders
diff --git a/lib/dry/initializer/builders/initializer.rb b/lib/dry/initializer/builders/initializer.rb
index 4c3d82e..941c40d 100644
--- a/lib/dry/initializer/builders/initializer.rb
+++ b/lib/dry/initializer/builders/initializer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Builders
@@ -41,15 +43,11 @@ def define_line
         end
 
         def params_lines
-          @definitions.reject(&:option)
-            .flat_map { |item| Attribute[item] }
-            .map { |line| "  " << line }
+          @definitions.reject(&:option).flat_map { Attribute[_1] }.map { "  #{_1}" }
         end
 
         def options_lines
-          @definitions.select(&:option)
-            .flat_map { |item| Attribute[item] }
-            .map { |line| "  " << line }
+          @definitions.select(&:option).flat_map { Attribute[_1] }.map { "  #{_1}" }
         end
 
         def end_line
diff --git a/lib/dry/initializer/builders/reader.rb b/lib/dry/initializer/builders/reader.rb
index ab23d48..37846fa 100644
--- a/lib/dry/initializer/builders/reader.rb
+++ b/lib/dry/initializer/builders/reader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Builders
diff --git a/lib/dry/initializer/builders/signature.rb b/lib/dry/initializer/builders/signature.rb
index c8c5fde..34f03cd 100644
--- a/lib/dry/initializer/builders/signature.rb
+++ b/lib/dry/initializer/builders/signature.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Builders
diff --git a/lib/dry/initializer/config.rb b/lib/dry/initializer/config.rb
index d97e882..b6d538a 100644
--- a/lib/dry/initializer/config.rb
+++ b/lib/dry/initializer/config.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     #
@@ -23,10 +25,10 @@ class Config
       # @return [Module] reference to the module to be included into class
       def mixin
         @mixin ||= Module.new.tap do |mod|
-          __dry_initializer__ = self
+          initializer = self
           mod.extend(Mixin::Local)
-          mod.send :define_method, :__dry_initializer_config__ do
-            __dry_initializer__
+          mod.define_method(:__dry_initializer_config__) do
+            initializer
           end
           mod.send :private, :__dry_initializer_config__
         end
diff --git a/lib/dry/initializer/definition.rb b/lib/dry/initializer/definition.rb
index 768de7d..b1d803e 100644
--- a/lib/dry/initializer/definition.rb
+++ b/lib/dry/initializer/definition.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     #
@@ -21,11 +23,11 @@ def options
           default: default,
           reader: reader,
           desc: desc
-        }.reject { |_, value| value.nil? }
+        }.compact
       end
 
       def name
-        @name ||= (option ? "option" : "parameter") << " '#{source}'"
+        @name ||= "#{option ? "option" : "parameter"} '#{source}'"
       end
       alias_method :to_s, :name
       alias_method :to_str, :name
diff --git a/lib/dry/initializer/dispatchers.rb b/lib/dry/initializer/dispatchers.rb
index c41092e..7e7952a 100644
--- a/lib/dry/initializer/dispatchers.rb
+++ b/lib/dry/initializer/dispatchers.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # The module is responsible for __normalizing__ arguments
 # of `.param` and `.option`.
 #
diff --git a/lib/dry/initializer/dispatchers/build_nested_type.rb b/lib/dry/initializer/dispatchers/build_nested_type.rb
index d4e3170..da9f009 100644
--- a/lib/dry/initializer/dispatchers/build_nested_type.rb
+++ b/lib/dry/initializer/dispatchers/build_nested_type.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Prepare nested data type from a block
 #
 # @example
@@ -56,8 +57,15 @@ def full_name(parent, name)
         end
 
         def build_struct(klass_name, block)
-          eval "class #{klass_name} < Dry::Initializer::Struct; end"
-          const_get(klass_name).tap { |klass| klass.class_eval(&block) }
+          # rubocop: disable Security/Eval
+          # rubocop: disable Style/DocumentDynamicEvalDefinition
+          eval <<~RUBY, TOPLEVEL_BINDING, __FILE__, __LINE__ + 1
+            class #{klass_name} < Dry::Initializer::Struct
+            end
+          RUBY
+          # rubocop: enable Style/DocumentDynamicEvalDefinition
+          # rubocop: enable Security/Eval
+          const_get(klass_name).tap { _1.class_eval(&block) }
         end
       end
     end
diff --git a/lib/dry/initializer/dispatchers/check_type.rb b/lib/dry/initializer/dispatchers/check_type.rb
index 3ad1cd8..9ef0952 100644
--- a/lib/dry/initializer/dispatchers/check_type.rb
+++ b/lib/dry/initializer/dispatchers/check_type.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Checks whether an unwrapped type is valid
 #
 module Dry
diff --git a/lib/dry/initializer/dispatchers/prepare_default.rb b/lib/dry/initializer/dispatchers/prepare_default.rb
index ef473f4..c1b9f21 100644
--- a/lib/dry/initializer/dispatchers/prepare_default.rb
+++ b/lib/dry/initializer/dispatchers/prepare_default.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Prepares the `:default` option
 #
 # It must respond to `.call` without arguments
diff --git a/lib/dry/initializer/dispatchers/prepare_ivar.rb b/lib/dry/initializer/dispatchers/prepare_ivar.rb
index 62f1ced..eb0aa5a 100644
--- a/lib/dry/initializer/dispatchers/prepare_ivar.rb
+++ b/lib/dry/initializer/dispatchers/prepare_ivar.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Prepares the variable name of a parameter or an option.
 #
 module Dry
diff --git a/lib/dry/initializer/dispatchers/prepare_optional.rb b/lib/dry/initializer/dispatchers/prepare_optional.rb
index deb545e..1933694 100644
--- a/lib/dry/initializer/dispatchers/prepare_optional.rb
+++ b/lib/dry/initializer/dispatchers/prepare_optional.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Defines whether an argument is optional
 #
 module Dry
diff --git a/lib/dry/initializer/dispatchers/prepare_reader.rb b/lib/dry/initializer/dispatchers/prepare_reader.rb
index 8b09cc3..2a0f375 100644
--- a/lib/dry/initializer/dispatchers/prepare_reader.rb
+++ b/lib/dry/initializer/dispatchers/prepare_reader.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Checks the reader privacy
 #
 module Dry
@@ -9,11 +10,11 @@ module PrepareReader
 
         def call(target: nil, reader: :public, **options)
           reader = case reader.to_s
-                  when "false", ""                      then nil
-                  when "true"                           then :public
-                  when "public", "private", "protected" then reader.to_sym
-                  else invalid_reader!(target, reader)
-                  end
+                   when "false", ""                      then nil
+                   when "true"                           then :public
+                   when "public", "private", "protected" then reader.to_sym
+                   else invalid_reader!(target, reader)
+                   end
 
           {target: target, reader: reader, **options}
         end
diff --git a/lib/dry/initializer/dispatchers/prepare_source.rb b/lib/dry/initializer/dispatchers/prepare_source.rb
index 460295f..fa6c778 100644
--- a/lib/dry/initializer/dispatchers/prepare_source.rb
+++ b/lib/dry/initializer/dispatchers/prepare_source.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # The dispatcher verifies a correctness of the source name
 # of param or option, taken as a `:source` option.
 #
diff --git a/lib/dry/initializer/dispatchers/prepare_target.rb b/lib/dry/initializer/dispatchers/prepare_target.rb
index 9e8c67f..dcbe366 100644
--- a/lib/dry/initializer/dispatchers/prepare_target.rb
+++ b/lib/dry/initializer/dispatchers/prepare_target.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Prepares the target name of a parameter or an option.
 #
 # Unlike source, the target must satisfy requirements for Ruby variable names.
diff --git a/lib/dry/initializer/dispatchers/unwrap_type.rb b/lib/dry/initializer/dispatchers/unwrap_type.rb
index 8114823..4604ac8 100644
--- a/lib/dry/initializer/dispatchers/unwrap_type.rb
+++ b/lib/dry/initializer/dispatchers/unwrap_type.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Looks at the `:type` option and counts how many nested arrays
 # it contains around either nil or a callable value.
 #
@@ -12,15 +13,19 @@ module UnwrapType
         extend self
 
         def call(type: nil, wrap: 0, **options)
-          type, wrap = unwrap(type, 0)
+          type, count = unwrap(type, wrap)
 
-          {type: type, wrap: wrap, **options}
+          {type: type, wrap: count, **options}
         end
 
         private
 
         def unwrap(type, count)
-          type.is_a?(Array) ? unwrap(type.first, count + 1) : [type, count]
+          if type.is_a?(::Array)
+            unwrap(type.first, count + 1)
+          else
+            [type, count]
+          end
         end
       end
     end
diff --git a/lib/dry/initializer/dispatchers/wrap_type.rb b/lib/dry/initializer/dispatchers/wrap_type.rb
index 56b31bb..b600928 100644
--- a/lib/dry/initializer/dispatchers/wrap_type.rb
+++ b/lib/dry/initializer/dispatchers/wrap_type.rb
@@ -1,4 +1,5 @@
-#
+# frozen_string_literal: true
+
 # Takes `:type` and `:wrap` to construct the final value coercer
 #
 module Dry
diff --git a/lib/dry/initializer/dsl.rb b/lib/dry/initializer/dsl.rb
index 0b403aa..592c802 100644
--- a/lib/dry/initializer/dsl.rb
+++ b/lib/dry/initializer/dsl.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     # Module-level DSL
@@ -37,8 +39,12 @@ def extended(klass)
         klass.include Mixin::Root
       end
 
-      def self.extended(mod)
-        mod.instance_variable_set :@null, UNDEFINED
+      class << self
+        private
+
+        def extended(mod)
+          mod.instance_variable_set :@null, UNDEFINED
+        end
       end
     end
   end
diff --git a/lib/dry/initializer/mixin.rb b/lib/dry/initializer/mixin.rb
index f54b00f..114bee5 100644
--- a/lib/dry/initializer/mixin.rb
+++ b/lib/dry/initializer/mixin.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     # @private
diff --git a/lib/dry/initializer/mixin/local.rb b/lib/dry/initializer/mixin/local.rb
index 3269727..30176f5 100644
--- a/lib/dry/initializer/mixin/local.rb
+++ b/lib/dry/initializer/mixin/local.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Mixin
diff --git a/lib/dry/initializer/mixin/root.rb b/lib/dry/initializer/mixin/root.rb
index 5e649c3..1a0cce1 100644
--- a/lib/dry/initializer/mixin/root.rb
+++ b/lib/dry/initializer/mixin/root.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module Mixin
diff --git a/lib/dry/initializer/struct.rb b/lib/dry/initializer/struct.rb
index 39ff1b6..576948b 100644
--- a/lib/dry/initializer/struct.rb
+++ b/lib/dry/initializer/struct.rb
@@ -1,9 +1,10 @@
-#
+# frozen_string_literal: true
+
 # The nested structure that takes nested hashes with indifferent access
 #
-class Dry
+module Dry
   module Initializer
-    module Struct
+    class Struct
       extend ::Dry::Initializer
 
       class << self
diff --git a/lib/dry/initializer/undefined.rb b/lib/dry/initializer/undefined.rb
index 12ebb21..7a6b901 100644
--- a/lib/dry/initializer/undefined.rb
+++ b/lib/dry/initializer/undefined.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
     module UNDEFINED
diff --git a/lib/dry/initializer/version.rb b/lib/dry/initializer/version.rb
index e68eee6..fc30664 100644
--- a/lib/dry/initializer/version.rb
+++ b/lib/dry/initializer/version.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module Dry
   module Initializer
-    VERSION = "3.1.0".freeze
+    VERSION = "3.1.0"
   end
 end
diff --git a/lib/tasks/benchmark.rake b/lib/tasks/benchmark.rake
index 044469c..acf9935 100644
--- a/lib/tasks/benchmark.rake
+++ b/lib/tasks/benchmark.rake
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 namespace :benchmark do
   desc "Runs benchmarks for plain params"
   task :plain_params do
diff --git a/lib/tasks/profile.rake b/lib/tasks/profile.rake
index 00c60a1..97ac766 100644
--- a/lib/tasks/profile.rake
+++ b/lib/tasks/profile.rake
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # rubocop: disable Lint/ConstantDefinitionInBlock
 namespace :profile do
   def profile(name, execution, &definition)