[ruby-core:72608] [Ruby trunk - Bug #11878] Comparison of prepended modules

[nobu@ruby-lang.org]

Issue #11878 has been updated by Nobuyoshi Nakada.

Description updated
Backport changed from 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN to 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED

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Bug #11878: Comparison of prepended modules
https://bugs.ruby-lang.org/issues/11878#change-55861

* Author: Tsuyoshi Sawada
* Status: Closed
* Priority: Normal
* Assignee: Nobuyoshi Nakada
* ruby -v: 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]
* Backport: 2.0.0: REQUIRED, 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED
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Including module `B` to class/module `A` gives the following results (as expected):

~~~ruby
module A; end
module B; end
A.include B
A < B # => true
B < A # => false
A <=> B # => -1
~~~

And prepending module `C` to `A` gives the following results:

~~~ruby
module C; end
A.prepend C
A < C # => true
C < A # => nil
A <=> C # => -1
~~~

It looks like including and prepending almost do not make difference with respect to module comparison, i.e., `A < B` and `A < C` are the same, and `A <=> B` and `A <=> C` are the same. However, then, the difference between `B < A` and `C < A` stands out unexplained. I suppose this is a bug. If `C < A` were to return `false`, then it would be at least consistent.

However, if that was what was intended, then at least to me, it is strange. In that case, I would like to make this a feature request. I would rather expect:

~~~ruby
A < C # => false
C < A # => true
A <=> C # => 1
~~~




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