module RuboCop::Cop::CheckMethods

def on_def(node) 

def on_def(node)
  method_name, args, body = *node
  check(node, method_name, args, body)
end

def on_defs(node) 

def on_defs(node)
  _scope, method_name, args, body = *node
  check(node, method_name, args, body)
end

def visibility_and_def_on_same_line?(receiver, method_name, args)

which are allowed in Ruby 2.1 and later.
private def my_method
Returns true for constructs such as 
def visibility_and_def_on_same_line?(receiver, method_name, args)
  !receiver &&
    [:public, :protected, :private,
     :module_function].include?(method_name) &&
    args.size == 1 && [:def, :defs].include?(args.first.type)
end