For slightly more future-proof monkey patches, raise an error if a method name starts being used upstream

def!.rb

# class SomethingYouDontControl
#   def! :something_you_expect_not_to_exist do |arg|
#     arg + 1
#   end
# end
#
# I wanted to provide built-in memoization, but it's not currenlty possible
# while preserving strict argument checking. https://bugs.ruby-lang.org/issues/9777
#
module Kernel
  def def! name, &block
    raise "`#{name}` already exists at #{instance_method(name).source_location}" if method_defined? name
    define_method name, &block
  end

  def singleton_def! name, &block
    singleton_class.def! name, &block
  end
end