use the module by including it instead of extending it

Author: esebastian

README.md

@@ -16,7 +16,7 @@ A simple module to provide value objects semantics to a class.
 require 'value_object'
 
 class Point
-  extend ValueObject
+  include ValueObject
   fields :x, :y
 end
 
@@ -39,7 +39,7 @@ point.x = 3
 require 'value_object'
 
 class Point
-  extend ValueObject
+  include ValueObject
   fields :x, :y
 end
 
@@ -71,7 +71,7 @@ a_point.eql?(a_different_point)
 require 'value_object'
 
 class Point
-  extend ValueObject
+  include ValueObject
   fields :x, :y
 end
 
@@ -99,7 +99,7 @@ You can declare invariants to restrict field values on initialization
 require 'value_object'
 
 class Point
-  extend ValueObject
+  include ValueObject
   fields :x, :y
   invariants :x_less_than_y, :inside_first_quadrant
 

lib/value_object.rb

@@ -1,89 +1,96 @@
 require 'exceptions'
 
 module ValueObject
-  def fields(*names)
-    raise NotDeclaredFields.new() if names.empty?()
 
-    attr_reader(*names)
+  def self.included(base)
+    base.extend(ClassMethods)
+  end
 
-    define_method(:initialize) do |*values|
-      check_fields_are_initialized(values)
-      set_instance_variables(values)
-      check_invariants()
-    end
+  module ClassMethods
+    def fields(*names)
+      raise NotDeclaredFields.new() if names.empty?()
 
-    define_method(:eql?) do |other|
-      self.class == other.class && values == other.values
-    end
+      attr_reader(*names)
 
-    define_method(:==) do |other|
-      eql?(other)
-    end
+      define_method(:initialize) do |*values|
+        check_fields_are_initialized(values)
+        set_instance_variables(values)
+        check_invariants()
+      end
 
-    define_method(:hash) do
-      self.class.hash ^ values.hash
-    end
+      define_method(:eql?) do |other|
+        self.class == other.class && values == other.values
+      end
 
-    define_method(:values) do
-      names.map { |field| send(field) }
-    end
-    protected(:values)
+      define_method(:==) do |other|
+        eql?(other)
+      end
 
-    define_method(:check_invariants) do
-    end
-    private(:check_invariants)
+      define_method(:hash) do
+        self.class.hash ^ values.hash
+      end
 
-    define_method(:check_fields_are_initialized) do |values|
-      raise WrongNumberOfArguments.new(names.length, values.length) unless arguments_number_is_right?(values)
-      raise FieldWithoutValue.new(uninitialized_fields_names(values)) unless all_fields_initialized?(values)
-    end
-    private(:check_fields_are_initialized)
+      define_method(:values) do
+        names.map { |field| send(field) }
+      end
+      protected(:values)
 
-    define_method(:arguments_number_is_right?) do |values|
-      fields_number = names.length
-      arguments_number = values.length
-      values.length == names.length
-    end
-    private(:arguments_number_is_right?)
+      define_method(:check_invariants) do
+      end
+      private(:check_invariants)
 
-    define_method(:uninitialized_fields) do |values|
-      names.zip(values).select { |name, value| value.nil? }
-    end
-    private(:uninitialized_fields)
+      define_method(:check_fields_are_initialized) do |values|
+        raise WrongNumberOfArguments.new(names.length, values.length) unless arguments_number_is_right?(values)
+        raise FieldWithoutValue.new(uninitialized_fields_names(values)) unless all_fields_initialized?(values)
+      end
+      private(:check_fields_are_initialized)
 
-    define_method(:all_fields_initialized?) do |values|
-      uninitialized_fields(values).empty?
-    end
-    private(:all_fields_initialized?)
+      define_method(:arguments_number_is_right?) do |values|
+        fields_number = names.length
+        arguments_number = values.length
+        values.length == names.length
+      end
+      private(:arguments_number_is_right?)
 
-    define_method(:uninitialized_fields_names) do |values|
-      uninitialized_fields(values).map { |field| field.first }
-    end
-    private(:uninitialized_fields_names)
+      define_method(:uninitialized_fields) do |values|
+        names.zip(values).select { |name, value| value.nil? }
+      end
+      private(:uninitialized_fields)
 
-    define_method(:set_instance_variables) do |values|
-      names.zip(values) do |name, value|
-        instance_variable_set(:"@#{name}", value)
+      define_method(:all_fields_initialized?) do |values|
+        uninitialized_fields(values).empty?
       end
-    end
-    private(:set_instance_variables)
-  end
+      private(:all_fields_initialized?)
+
+      define_method(:uninitialized_fields_names) do |values|
+        uninitialized_fields(values).map { |field| field.first }
+      end
+      private(:uninitialized_fields_names)
 
-  def invariants(*predicate_symbols)
-    define_method(:check_invariants) do
-      predicate_symbols.each do |predicate_symbol|
-        valid = invariant_holds?(predicate_symbol)
-        raise ViolatedInvariant.new(predicate_symbol, self.values) unless valid
+      define_method(:set_instance_variables) do |values|
+        names.zip(values) do |name, value|
+          instance_variable_set(:"@#{name}", value)
+        end
       end
+      private(:set_instance_variables)
     end
 
-    define_method(:invariant_holds?) do |predicate_symbol|
-      begin
-        valid = send(predicate_symbol)
-      rescue
-        raise NotImplementedInvariant.new(predicate_symbol)
+    def invariants(*predicate_symbols)
+      define_method(:check_invariants) do
+        predicate_symbols.each do |predicate_symbol|
+          valid = invariant_holds?(predicate_symbol)
+          raise ViolatedInvariant.new(predicate_symbol, self.values) unless valid
+        end
+      end
+
+      define_method(:invariant_holds?) do |predicate_symbol|
+        begin
+          valid = send(predicate_symbol)
+        rescue
+          raise NotImplementedInvariant.new(predicate_symbol)
+        end
       end
+      private(:invariant_holds?)
     end
-    private(:invariant_holds?)
   end
 end

spec/value_object_spec.rb

@@ -5,7 +5,7 @@
 
   describe "standard behavior" do
     class Point
-      extend ValueObject
+      include ValueObject
       fields :x, :y
     end
 
@@ -62,7 +62,7 @@ class Point
 
       it "must have number of values equal to number of fields" do
         class Point
-          extend ValueObject
+          include ValueObject
           fields :x, :y
         end
 
@@ -80,7 +80,7 @@ class Point
   describe "forcing invariants" do
     it "forces declared invariants" do
       class Point
-        extend ValueObject
+        include ValueObject
         fields :x, :y
         invariants :x_less_than_y, :inside_first_quadrant