Ruby

Ah, I didn't know initialize is always private:

irb(main):001:0> class A irb(main):002:1> def initialize irb(main):003:2> end irb(main):004:1> end => :initialize irb(main):005:0> A.new.initialize Traceback (most recent call last): 4: from /opt/rubies/2.6.1/bin/irb:23:in `<main>' 3: from /opt/rubies/2.6.1/bin/irb:23:in `load' 2: from /opt/rubies/2.6.1/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>' 1: from (irb):5 NoMethodError (private method `initialize' called for #<A:0x00007faedb0bf428>) 

I think this fact should be documented at least.

I think it is documented somewhere, but can't remember where it is now.

Anyway, these methods are always defined as private, unless singleton methods.
initialize, initialize_copy, initialize_clone, initialize_dup, respond_to_missing?

This behavior is from [Feature #6539]. Do you remember why these methods are made to be always private, instead of setting them to be private in Kernel only?
I don't think this rule make sense for BasicObject classes since they don't have #dup and #clone and #respond_to?:

class A < BasicObject public def initialize_dup end end A.new.initialize_dup # private method `initialize_dup' called 

initialize isn't involved in [Feature #6539].
It has been always private since more earlier days, 1.1 at least.