Ruby: see source code of a method

https://stackoverflow.com/questions/3393096/how-can-i-get-source-code-of-a-method-dynamically-and-also-which-file-is-this-me

  $ rails console
  > require 'method_source'
  > I18n::Backend::Simple.instance_method(:lookup).source.display

class A
  def foo
  end
end

file, line = A.instance_method(:foo).source_location
# or
file, line = A.new.method(:foo).source_location