[ruby-core:61120] [ruby-trunk - Bug #9573] descendants of a module don't gain its future ancestors, but descendants of a class, do

Issue #9573 has been updated by First Last.


Nobuyoshi Nakada wrote:
> First Last wrote:
> > so 2 issues:
> > 
> > 1. It would seem natural that in dynamic language, dynamically added ancestors should propagate to descendants
> 
> It's a longstanding issue, a descendant knows its ancestors, but an ancestor doesn't know its descendants.

Is it the case the ancestors are cached in each descendant?  So that it does not actually walk the ancestor tree each time.  If so, is there any way to invalidate this cache for a given class or all, and have it reevaluate the ancestors?

> 
> > 2. Why is there a difference in ancestor propagation between modules and classes
> 
> It is not between modules and classes, but caused by the order of inheritance and including.

Please clarify.  Mod1 is included in Class1 after Class2 extends Class1 and yet Class2 somehow learns of it's new grandparent, Mod1.  How does that happen if ancestors (Class1) do not know their descendants (Class2)

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Bug #9573: descendants of a module don't gain its future ancestors, but descendants of a class, do
https://bugs.ruby-lang.org/issues/9573#change-45503

* Author: First Last
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.1.1p76 (2014-02-24 revision 45161) [i686-linux]
* Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN
----------------------------------------
```ruby
module Mod1
end

module Mod2
end

class Class1
end

class Class2 < Class1
end

p Class2.ancestors - Object.ancestors # [Class2, Class1]

Class1.include Mod1

p Class2.ancestors - Object.ancestors # [Class2, Class1, Mod1]

Mod1.include Mod2

p Mod1.ancestors - Object.ancestors # [Mod1, Mod2]

p Class2.ancestors - Object.ancestors # [Class2, Class1, Mod1]
```
________________________________________________________________

note that descendants of a class do gain its future ancestors

so 2 issues:

1. It would seem natural that in dynamic language, dynamically added ancestors should propagate to descendants
2. Why is there a difference in ancestor propagation between modules and classes
 



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