Forum: Ruby-core descendants of a module don't gain its future ancestors, but descendants of a class, do

F1d6cc2b735bfd82c8773172da2aeab9?d=identicon&s=25 Nobuyoshi Nakada (nobu)
on 2014-02-27 07:24
(Received via mailing list)
Issue #9573 has been updated by Nobuyoshi Nakada.

Description updated

First Last wrote:
> so 2 issues:
>
> 1. It would seem natural that in dynamic language, dynamically added ancestors
should propagate to descendants

It's longstanding issue, a descendant knows its ancestors, but an
ancestor doesn't know its descendants.

> 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.


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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-45502

* 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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