Adds MergeInitializer extension.

README.markdown

@@ -20,7 +20,10 @@ below. This provides maximum flexibility for users to mix and match
 functionality while maintaining feature parity with earlier versions of
 Hashie.
 
-### Hashie::Extensions::Coercion
+Any of the extensions listed below can be mixed into a class by
+`include`-ing `Hashie::Extensions::ExtensionName`.
+
+### Coercion
 
 Coercions allow you to set up "coercion rules" based either on the key
 or the value type to massage data as it's being inserted into the Hash.
@@ -53,14 +56,16 @@ Hash-like class that is self-propagating.
       end
     end
 
-### Hashie::Extensions::KeyConversion
+### KeyConversion
 
 The KeyConversion extension gives you the convenience methods of
 `symbolize_keys` and `stringify_keys` along with their bang
 counterparts. You can also include just stringify or just symbolize with
 `Hashie::Extensions::StringifyKeys` or `Hashie::Extensions::SymbolizeKeys`.
 
-### Hashie::Extensions::MethodAccess
+### MergeInitializer
+
+### MethodAccess
 
 The MethodAccess extension allows you to quickly build method-based
 reading, writing, and querying into your Hash descendant. It can also be
@@ -76,12 +81,12 @@ included as individual modules, i.e. `Hashie::Extensions::MethodReader`,
     h.abc  # => 'def'
     h.abc? # => true
 
-### Hashie::Extensions::DeepMerge (Unimplemented)
+### DeepMerge (Unimplemented)
 
 This extension *will* allow you to easily include a recursive merging
 system to any Hash descendant.
 
-### Hashie::Extensions::IndifferentAccess (Unimplemented)
+### IndifferentAccess (Unimplemented)
 
 This extension *will* allow you to easily give a hash rules for
 normalizing keys, for instance to allow symbol or string keys both to

lib/hashie.rb

@@ -12,6 +12,7 @@ module Extensions
     autoload :DeepMerge,         'hashie/extensions/deep_merge'
     autoload :KeyConversion,     'hashie/extensions/key_conversion'
     autoload :IndifferentAccess, 'hashie/extensions/indifferent_access'
+    autoload :MergeInitializer,  'hashie/extensions/merge_initializer'
     autoload :MethodAccess,      'hashie/extensions/method_access'
     autoload :MethodQuery,       'hashie/extensions/method_access'
     autoload :MethodReader,      'hashie/extensions/method_access'

lib/hashie/extensions/merge_initializer.rb

@@ -0,0 +1,24 @@
+module Hashie
+  module Extensions
+    # The MergeInitializer is a super-simple mixin that allows
+    # you to initialize a subclass of Hash with another Hash
+    # to give you faster startup time for Hash subclasses. Note
+    # that you can still provide a default value as a second
+    # argument to the initializer.
+    #
+    # @example
+    #   class MyHash < Hash
+    #     include Hashie::Extensions::MergeInitializer
+    #   end
+    #
+    #   h = MyHash.new(:abc => 'def')
+    #   h[:abc] # => 'def'
+    #
+    module MergeInitializer
+      def initialize(hash = {}, default = nil, &block)
+        super(default, &block)
+        update(hash)
+      end
+    end
+  end
+end

spec/hashie/extensions/merge_initializer_spec.rb

@@ -0,0 +1,20 @@
+require 'spec_helper'
+
+describe Hashie::Extensions::MergeInitializer do
+  class MergeInitializerHash < Hash; include Hashie::Extensions::MergeInitializer end
+  subject{ MergeInitializerHash }
+
+  it 'should initialize fine with no arguments' do
+    subject.new.should == {}
+  end
+
+  it 'should initialize with a hash' do
+    subject.new(:abc => 'def').should == {:abc => 'def'}
+  end
+
+  it 'should initialize with a hash and a default' do
+    h = subject.new({:abc => 'def'}, 'bar')
+    h[:foo].should == 'bar'
+    h[:abc].should == 'def'
+  end
+end