Dup default value on evaluate rather than on initialization

Issue #25

lib/virtus/attribute/default_value.rb

@@ -29,8 +29,7 @@ class DefaultValue
       #
       # @api private
       def initialize(attribute, value)
-        @attribute = attribute
-        @value     = case value when *DUP_CLASSES then value else value.dup end
+        @attribute, @value = attribute, value
       end
 
       # Evaluates the value
@@ -41,7 +40,13 @@ def initialize(attribute, value)
       #
       # @api private
       def evaluate(instance)
-        callable? ? call(instance) : value
+        if callable?
+          call(instance)
+        elsif duplicable?
+          value.dup
+        else
+          value
+        end
       end
 
     private
@@ -66,6 +71,15 @@ def callable?
         value.respond_to?(:call)
       end
 
+      # Returns whether or not the value is duplicable
+      #
+      # # return [TrueClass, FalseClass]
+      #
+      # @api private
+      def duplicable?
+        case value when *DUP_CLASSES then false else true end
+      end
+
     end # class DefaultValue
   end # class Attribute
 end # module Virtus

spec/unit/virtus/attribute/default_value/class_methods/new_spec.rb

@@ -5,18 +5,15 @@
 
   let(:attribute) { Virtus::Attribute::String.new(:attribute) }
 
-  context 'with a value that can be duped' do
+  context 'with a duplicable value' do
     let(:value) { 'something' }
-
-    its(:value) { should     eql(value)   }
-    its(:value) { should_not equal(value) }
+    its(:value) { should equal(value) }
   end
 
-  context 'with a value that cannot be duped' do
+  context 'with a non-duplicable value' do
     [ nil, true, false, 1, :symbol ].each do |value|
       context "with #{value.inspect}" do
         let(:value) { value }
-
         its(:value) { should equal(value) }
       end
     end

spec/unit/virtus/attribute/default_value/instance_methods/evaluate_spec.rb

@@ -8,8 +8,16 @@
   let(:instance)  { Class.new }
 
   context 'with a non-callable value' do
-    let(:value) { 'something' }
-    it { should eql(value) }
+    context 'with a non-duplicable value' do
+      let(:value) { nil }
+      it { should eql(value) }
+    end
+
+    context 'with a duplicable value' do
+      let(:value) { 'something' }
+      it { should     eql(value) }
+      it { should_not equal(value)}
+    end
   end
 
   context 'with a callable value' do