Map over a Ruby hash, replacing the values for each key.

gistfile1.rb

# Map over a hash, replacing the values for each key.
x = {:a => 1, :b => 2}
#=> {:a => 1, :b => 2}
x.merge(x) { |k, v| v * 2 }
#=> {:a => 2, :b => 4}

# If you want to replace Enumerable's map...
class Hash
  def map(&block)
    merge(self, &block)
  end
end

# then...
x.map { |k, v| v * 2 }
#=> {:a => 2, :b => 4}