Feature #8026: Need Module#prepended_modules

• Status: Feedback
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[marcandre (Marc-Andre Lafortune)]

We should have a way to get the list of prepended modules of a class or module.

module Mixin
end

module Outer
  prepend Mixin
end

Mixin.prepended_modules   #=> []
Outer.prepended_modules   #=> [Mixin]

See also bug #8025.

[matz (Yukihiro Matsumoto)]

I am OK with the idea.

Matz.

[knu (Akinori MUSHA)]

What about adding Module#prepend?(other) also, which could be implemented in ruby as follows?

module Module
def prepend?(other)
ancestors.find { |mod|
break false if mod == self
mod == other
}
end
end

[marcandre (Marc-Andre Lafortune)]

• File prepended.pdf prepended.pdf added

Slide added. I'm also proposing an optional flag to search only the receiver and not the ancestors.

I didn't put in prepend? but it should also be added. On the other hand, Array.prepend?(Enumerable) should return false, no?

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Feedback

I basically accept the idea.

But according to the slide, the optional include_ancestors is true, but it does mean cherry-picking prepended modules from ancestor list. I cannot think of any use case of this behavior.

Matz.

[hsbt (Hiroshi SHIBATA)]

• Target version changed from 2.1.0 to 2.2.0

[nobu (Nobuyoshi Nakada)]

• Has duplicate Feature #11879: `Module#prepended_modules` added

[naruse (Yui NARUSE)]

• Target version deleted (2.2.0)

[mame (Yusuke Endoh)]

matz (Yukihiro Matsumoto) wrote:

But according to the slide, the optional include_ancestors is true, but it does mean cherry-picking prepended modules from ancestor list. I cannot think of any use case of this behavior.

I guess include_ancestors here means "modules prepended by prepended modules":

module A; end
module B; prepend A; end
module C; prepend B; end

C.prepended_modules(true)  #=> [A, B]
C.prepended_modules(false) #=> [B]

So, include_ancestors is not a good name; should it be called include_descendants?

@marcandre (Marc-Andre Lafortune) , am I right?

[mame (Yusuke Endoh)]

Now I'm unsure if the feature is worth adding. It was accepted six years ago, but not implemented yet. I've never heard any actual trouble due to the lack.

[matz (Yukihiro Matsumoto)]

I am still OK with the idea (but not for ancestors). prepended_modules should list direct prepended modules for the receiver.

Matz.