当引用失败Object.const_defined？的常量时，它不会调用const_missing

Question

I am hitting a problem that a constant is being mapped to a wrong file. When debugging it, it shows weird things:

=> 1: class App::CloudCredential < App::Credential
   2: end
(byebug) Object.const_defined? "App::Credential"
false
(byebug) App::Credential
App::Shared::Credential
(byebug) App::Credential.class
Module
(byebug) App::Credential.name
"App::Shared::Credential" 

My questions are that when Object.const_defined? "App::Credential" Object.const_defined? "App::Credential" returns false ,

1. why this wouldn't lead to const_missing ?
2. why referencing it still print something (which is wrong) as if the constant is defined (against what Object.const_defined? tells me)
3. Basically I'd like to know under what situation (or what kind of test I can use in byebug ) that would lead to const_missing . I am trying to find out why this App::Credential is being mapped to a complete wrong file (that of App::Shared::Credential )

More information: This App::Shared::Credential is actually a module that is being included from the class App::Credential and this App::Shared::Credential has been included by another class.

Thanks

Answer 1

What you describe is not inconsistent at all.

When you try to access App::Credential , you are looking it up in the current constant namespace, but when you are using const_defined? , you are explicitly asking Object whether the constant is defined there . But App::Credential could be defined in a subclass of Object , not in Object directly, and then this would return false .

module Foo
  module Bar
    Baz = 42
  end

  const_defined? 'Bar::Baz'
  #=> true

  Object.const_defined? 'Bar::Baz'
  #=> false
end

Since you are looking in two different places, it is perfectly sensible to get two different answers.