Issue #12834 has been updated by marcandre (Marc-Andre Lafortune).


shyouhei (Shyouhei Urabe) wrote:
> Thus, matz started thinking that if a module is prepended multiple times, that should appear more than once in a method chain.

Could you clarify?

For inclusion/prepending, there are two questions in my mind:
1) what happens if a module is included/prepended multiple times at different places in the hierarchy (e.g. in A and B, in the example above)
2) what happens if it is included/prepended multiple times at the same level (e.g. twice in A)

Was the discussion about (b) allowing multiple times at the same level?



----------------------------------------
Bug #12834: `prepend` getting prepended even if it already exists in the ancestors chain
https://bugs.ruby-lang.org/issues/12834#change-68056

* Author: ndn (Nikola Nenkov)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.3.1
* Backport: 2.3: UNKNOWN
----------------------------------------
```
module M; end
class A; prepend M; end
class B < A; prepend M; end

B.ancestors # => [M, B, M, A, Object, Kernel, BasicObject]
```

Even though I find this behaviour to be more intuitive, it is inconsistent with `Module#include` and is potentially breaking.
I didn't see a mention on the [[release notes]](https://www.ruby-lang.org/en/news/2015/12/25/ruby-2-3-0-released/) and the [[documentation]](https://ruby-doc.org/core-2.3.1/Module.html#method-i-prepend_features) is now outdated. 



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