Fix Dash#merge!

lib/hashie/dash.rb

@@ -135,6 +135,13 @@ def merge(other_hash)
       new_dash
     end
 
+    def merge!(other_hash)
+      other_hash.each do |k,v|
+        self[k] = block_given? ? yield(k, self[k], v) : v
+      end
+      self
+    end
+
     def replace(other_hash)
       other_hash = self.class.defaults.merge(other_hash)
       (keys - other_hash.keys).each { |key| delete(key) }

spec/hashie/dash_spec.rb

@@ -176,6 +176,35 @@ class DeferredTest < Hashie::Dash
     end
   end
 
+  describe '#merge!' do
+    it 'modifies the existing instance of the Dash' do
+      original_dash = subject.merge!(:first_name => 'Robert')
+      subject.object_id.should == original_dash.object_id
+    end
+
+    it 'merges the given hash' do
+      subject.merge!(:first_name => 'Robert', :email => 'robert@example.com')
+      subject.first_name.should == 'Robert'
+      subject.email.should == 'robert@example.com'
+    end
+
+    it 'fails with non-existent properties' do
+      expect { subject.merge!(:middle_name => 'James') }.to raise_error(NoMethodError)
+    end
+
+    it 'errors out when attempting to set a required property to nil' do
+      expect { subject.merge!(:first_name => nil) }.to raise_error(ArgumentError)
+    end
+
+    context "given a block" do
+      it "sets merged key's values to the block's return value" do
+        subject.merge!(:first_name => 'Jim') do |key, oldval, newval|
+          "#{key}: #{newval} #{oldval}"
+        end.first_name.should == 'first_name: Jim Bob'
+      end
+    end
+  end
+
   describe 'properties' do
     it 'lists defined properties' do
       described_class.properties.should == Set.new([:first_name, :email, :count])