* Make code "Object Shape friendly"

https://island94.org/2023/10/writing-object-shape-friendly-code-in-ruby

lib/contracted_value/core.rb

@@ -231,6 +231,8 @@ def initialize(input_attr_values = {})
           )
         end
 
+      @attr_values = {}
+
       self.class.send(:attribute_set).each_attribute do |attribute|
         attr_value = attribute.extract_value(input_attr_values_hash)
 
@@ -253,8 +255,8 @@ def initialize(input_attr_values = {})
 
         # Using symbol since attribute names are limited in number
         # An alternative would be using frozen string
-        instance_variable_set(
-          :"@#{attribute.name}",
+        @attr_values.store(
+          attribute.name.to_sym,
           sometimes_frozen_attr_value,
         )
       end
@@ -265,10 +267,7 @@ def initialize(input_attr_values = {})
     # rubocop:enable Metrics/CyclomaticComplexity
 
     def to_h
-      self.class.send(:attribute_set).
-        each_attribute.each_with_object({}) do |attribute, hash|
-          hash[attribute.name] = instance_variable_get(:"@#{attribute.name}")
-        end
+      @attr_values.clone
     end
 
     # == Class interface == #
@@ -297,7 +296,7 @@ def attribute(
         )
         @attribute_set = @attribute_set.add(attr)
 
-        attr_reader(name)
+        define_method(name) { @attr_values[name.to_sym] }
       end
 
       # @api private

spec/contracted_value/value_spec.rb

@@ -93,13 +93,19 @@
 
         it "does not raise error when input is a value" do
           aggregate_failures do
+            new_val = nil
             expect {
-              value_class.new(
+              new_val = value_class.new(
                 value_class.new(
                   default_inputs,
                 ),
               )
             }.to_not raise_error
+            if new_val
+              default_inputs.each_pair do |attr_name, attr_val|
+                expect(new_val.public_send(attr_name)).to eq(attr_val)
+              end
+            end
           end
         end