Check for an existing method in the current class before extending. IF the method already exists, then a warning is printed and the extension is not added. Otherwise the block is yielded and any definitions in the block will take effect.

Usage:

class String
  rake_extension("xyz") do
    def xyz
      ...
    end
  end
end

Source Code

# File rake.rb, line 60
def rake_extension(method)
  if instance_methods.include?(method.to_s) || instance_methods.include?(method.to_sym)
    $stderr.puts "WARNING: Possible conflict with Rake extension: #{self}##{method} already exists"
  else
    yield
  end
end