Issue #9573 has been updated by First Last.


Jeremy Evans wrote:
> 
> Ruby doesn't have multiple inheritance.  Ruby method lookup uses a linked listed, not a tree.  This is the reason for iclasses, and why including module B in module A after A has been included in class C does not include B in C.
> 

Conceptually Ruby does have multiple inheritance, an object is_a?(all included modules).

Is MRI's iclass snapshotting an implementation detail?  Can it theoretically be done differently (e.g. tree that you mentioned)


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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-45771

* 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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