Introduce Hashie::Extensions::Dash::Coercion.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 * Your contribution here.
 * [#304](https://github.com/intridea/hashie/pull/304): Ensured compatibility of `Hash` extensions with singleton objects - [@regexident](https://github.com/regexident).
+* [#306](https://github.com/intridea/hashie/pull/306): Added Hashie::Extensions::Dash::Coercion - [@marshall-lee](https://github.com/marshall-lee).
 
 ## 3.4.2 (6/2/2015)
 

README.md

@@ -607,6 +607,36 @@ model.created_at.class  #=> Time
 
 To enable compatibility with Rails 4 use the [hashie-forbidden_attributes](https://github.com/Maxim-Filimonov/hashie-forbidden_attributes) gem.
 
+### Dash Extension: Coercion.
+
+If you want to use `Hashie::Extensions::Coercion` together with `Dash` then
+you may probably want to use `Hashie::Extensions::Dash::Coercion` instead.
+This extension automatically includes `Hashie::Extensions::Coercion`
+and also adds a convenient `:coerce` option to `property` so you can define coercion in one line
+instead of using `property` and `coerce_key` separate:
+
+```ruby
+class UserHash < Hashie::Dash
+  include Hashie::Extensions::Coercion
+
+  property :id
+  property :posts
+
+  coerce_key :posts, Array[PostHash]
+end
+```
+
+This is the same as:
+
+```ruby
+class UserHash < Hashie::Dash
+  include Hashie::Extensions::Dash::Coercion
+
+  property :id
+  property :posts, coerce: Array[PostHash]
+end
+```
+
 ## Trash
 
 A Trash is a Dash that allows you to translate keys on initialization. It mixes

lib/hashie.rb

@@ -34,6 +34,7 @@ module Hashie
     module Dash
       autoload :IndifferentAccess, 'hashie/extensions/dash/indifferent_access'
       autoload :PropertyTranslation, 'hashie/extensions/dash/property_translation'
+      autoload :Coercion, 'hashie/extensions/dash/coercion'
     end
 
     module Mash

lib/hashie/extensions/dash/coercion.rb

@@ -0,0 +1,25 @@
+module Hashie
+  module Extensions
+    module Dash
+      module Coercion
+        # Extends a Dash with the ability to define coercion for properties.
+
+        def self.included(base)
+          base.send :include, Hashie::Extensions::Coercion
+          base.extend ClassMethods
+        end
+
+        module ClassMethods
+          # Defines a property on the Dash. Options are the standard
+          # <tt>Hashie::Dash#property</tt> options plus:
+          #
+          # * <tt>:coerce</tt> - The class into which you want the property coerced.
+          def property(property_name, options = {})
+            super
+            coerce_key property_name, options[:coerce] if options[:coerce]
+          end
+        end
+      end
+    end
+  end
+end

spec/hashie/extensions/dash/coercion_spec.rb

@@ -0,0 +1,13 @@
+require 'spec_helper'
+
+describe Hashie::Extensions::Dash::Coercion do
+  class DashWithCoercion < Hashie::Dash
+    include Hashie::Extensions::Dash::Coercion
+
+    property :type, coerce: Symbol
+  end
+
+  it 'does the coercion of properties' do
+    expect(DashWithCoercion.new(type: 'something')).to eq(type: :something)
+  end
+end