Merge pull request #271 from gregory/defaults_based_on_self

provide self as context when evaluating default

3 files changed, 16 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 970b66f..4333585 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,6 @@
 ## Next
 
+* [#271](https://github.com/intridea/hashie/pull/271): Added ability to define defaults based on current hash - [@gregory](https://github.com/gregory).
 * [#247](https://github.com/intridea/hashie/pull/247): Fixed #stringify_keys and #symbolize_keys collision with ActiveSupport - [@bartoszkopinski](https://github.com/bartoszkopinski).
 * [#249](https://github.com/intridea/hashie/pull/249): SafeAssignment will now also protect hash-style assignments - [@jrochkind](https://github.com/jrochkind).
 * [#251](https://github.com/intridea/hashie/pull/251): Added block support to indifferent access #fetch - [@jgraichen](https://github.com/jgraichen).
diff --git a/lib/hashie/dash.rb b/lib/hashie/dash.rb
index 849629f..cc20a93 100644
--- a/lib/hashie/dash.rb
+++ b/lib/hashie/dash.rb
@@ -96,7 +96,8 @@ module Hashie
 
       self.class.defaults.each_pair do |prop, value|
         self[prop] = begin
-          value.dup
+          val = value.dup
+          val.is_a?(Proc) && val.arity > 0 ? val.call(self) : val
         rescue TypeError
           value
         end
diff --git a/spec/hashie/dash_spec.rb b/spec/hashie/dash_spec.rb
index 1d44d5a..1de533f 100644
--- a/spec/hashie/dash_spec.rb
+++ b/spec/hashie/dash_spec.rb
@@ -46,6 +46,11 @@ class DeferredTest < Hashie::Dash
   property :created_at, default: proc { Time.now }
 end
 
+class DeferredWithSelfTest < Hashie::Dash
+  property :created_at, default: -> { Time.now }
+  property :updated_at, default: ->(test) { test.created_at }
+end
+
 describe DashTest do
   def property_required_error(property)
     [ArgumentError, "The property '#{property}' is required for #{subject.class.name}."]
@@ -168,6 +173,14 @@ describe DashTest do
     end
   end
 
+  context 'reading from a deferred property based on context' do
+    it 'provides the current hash as context for evaluation' do
+      deferred = DeferredWithSelfTest.new
+      expect(deferred[:created_at].object_id).to eq deferred[:created_at].object_id
+      expect(deferred[:updated_at].object_id).to eq deferred[:created_at].object_id
+    end
+  end
+
   describe '#new' do
     it 'fails with non-existent properties' do
       expect { described_class.new(bork: '') }.to raise_error(*no_property_error('bork'))