Feature #11927: Return value for `Module#include` and `Module#prepend`

• Status: Open
• Assignee: -
• Target version: -

[sawa (Tsuyoshi Sawada)]

Currently, Module#include and Module#prepend return the receiver, regardless of whether the ancestor chain has been modified. It is not straightforward to know whether it actually had effect.

module A; end
module B; end
A.include B # => A
A.ancestors # => [A, B]
A.prepend B # => A
A.ancestors # => [A, B]

I propose that, when Module#include and Module#prepend have no effect, they should either:

(1) return nil
(2) return false, or
(3) raise an exception

This is similar to Kernel#require, which returns false when it has no effect. To make it parallel with Kernel#require, it might be even better to return true when Module#include and Module#prepend have effect, and false otherwise. It makes no sense to return the receiver because that is known.

Some relevant cases with expectations are:

• prepend after include

module A; end
module B; end
A.include B # => A/true
A.prepend B # => nil/false/exception

• include after prepend

module A; end
module B; end
A.prepend B # => A/true
A.include B # => nil/false/exception

• include/prepend after include/include at superclass

class A; end
module B; end
A.include M # => A/true
class B < A; end
B.include M # => nil/false/exception

[fatkodima (Dima Fatko)]

I would like to have this. Please, reconsider this feature.

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[sawa (Tsuyoshi Sawada)]

• Description updated (diff)

[marcandre (Marc-Andre Lafortune)]

It would help to:

1. have an example of use case

2. discuss why B.include M unless B < M is not equivalent / sufficient