Ruby

It's not just String.

Array.instance_method(:a).owner # => Object 

Those results were from IRB. Here's my results from a Ruby script.

"test_scope_creep.rb"

puts "".methods.count puts defined? "".a def a "foo" end puts "".methods.count puts defined? "".a puts String.private_method_defined? :a puts String.instance_method(:a).owner puts "".send :a puts Array.private_method_defined? :a puts Array.instance_method(:a).owner puts [].send :a 

Output:

170 170 true Object foo true Object foo 

It appears they are defined as private methods when run via ruby and in irb they run like they're not private methods.

It's not really a bug.

When you define following method. It is added on Object class. And any class which inherits from Object class will have following method.

You can try calling following method on any class which inherits Object class, you should get same output.

def a "foo" end