1  module ActiveSupport #:nodoc:
   2    module CoreExtensions #:nodoc:
   3      module Hash #:nodoc:
   4        # Allows for reverse merging two hashes where the keys in the calling hash take precedence over those
   5        # in the <tt>other_hash</tt>. This is particularly useful for initializing an option hash with default values:
   6        #
   7        #   def setup(options = {})
   8        #     options.reverse_merge! :size => 25, :velocity => 10
   9        #   end
  10        #
  11        # Using <tt>merge</tt>, the above example would look as follows:
  12        #
  13        #   def setup(options = {})
  14        #     { :size => 25, :velocity => 10 }.merge(options)
  15        #   end
  16        #
  17        # The default <tt>:size</tt> and <tt>:velocity</tt> are only set if the +options+ hash passed in doesn't already
  18        # have the respective key.
  19        module ReverseMerge
  20          # Performs the opposite of <tt>merge</tt>, with the keys and values from the first hash taking precedence over the second.
  21          def reverse_merge(other_hash)
  22            other_hash.merge(self)
  23          end
  24 
  25          # Performs the opposite of <tt>merge</tt>, with the keys and values from the first hash taking precedence over the second.
  26          # Modifies the receiver in place.
  27          def reverse_merge!(other_hash)
  28            replace(reverse_merge(other_hash))
  29          end
  30 
  31          alias_method :reverse_update, :reverse_merge!
  32        end
  33      end
  34    end
  35  end