Add ability to use lambdas with format_with options.

Author: Robert Ross

lib/grape/entity.rb

@@ -203,7 +203,11 @@ def value_for(attribute, options = {})
       elsif exposure_options[:using]
         exposure_options[:using].represent(object.send(attribute), :root => nil)
       elsif exposure_options[:format_with]
-        self.send(exposure_options[:format_with].to_sym, object.send(attribute))
+        if exposure_options[:format_with].is_a? Symbol
+          self.send(exposure_options[:format_with].to_sym, object.send(attribute))
+        elsif exposure_options[:format_with].respond_to? :call
+          exposure_options[:format_with].call(object.send(attribute))
+        end
       else
         object.send(attribute)
       end

spec/grape/entity_spec.rb

@@ -204,9 +204,10 @@
       :name => 'Bob Bobson', 
       :email => '[email protected]',
       :birthday => Time.new(2012, 2, 27),
+      :fantasies => ['Unicorns', 'Double Rainbows', 'Nessy'],
       :friends => [
-        mock(:name => "Friend 1", :email => '[email protected]', :birthday => Time.new(2012, 2, 27), :friends => []), 
-        mock(:name => "Friend 2", :email => '[email protected]', :birthday => Time.new(2012, 2, 27), :friends => [])
+        mock(:name => "Friend 1", :email => '[email protected]', :fantasies => [], :birthday => Time.new(2012, 2, 27), :friends => []), 
+        mock(:name => "Friend 2", :email => '[email protected]', :fantasies => [], :birthday => Time.new(2012, 2, 27), :friends => [])
       ]
     } }
     subject{ fresh_class.new(model) }
@@ -236,6 +237,8 @@
           def timestamp(date)
             date.strftime('%m/%d/%Y')
           end
+
+          expose :fantasies, :format_with => lambda {|f| f.reverse }
         end
       end
 
@@ -272,6 +275,10 @@ class FriendEntity < Grape::Entity
       it 'should return a formatted value if format_with is passed' do
         subject.send(:value_for, :birthday).should == '02/27/2012'
       end
+
+      it 'should return a formatted value if format_with is passed a lambda' do
+        subject.send(:value_for, :fantasies).should == ['Nessy', 'Double Rainbows', 'Unicorns']
+      end
     end
 
     describe '#key_for' do