[ruby-core:103382] [Ruby master Feature#17753] Add Module#namespace

Issue #17753 has been updated by fxn (Xavier Noria).


Also, in case my comments above are too genric, let's take the use case in the description of the ticket:

> I can do A::B::C.outer_scope.constants to find the list of "sibling" constants to C.

Let's consider

```ruby
module A
  module B
    class C; end
    class D; end
  end 
end

module X
  Y = A::B::C
  Z = 1
end
```

In what sense is `A::B::D` a sibling of `A::B::C` and `X::Z` is not?

If our input is a class object, as in the `ObjectSpace` example, you have no information that allows you to jump from it to its possibly multiple places in which the object may be stored. And the original constant may be gone, those places can be elsewhere (as it happens with stale class objects cached during Rails initialization after a reload).

On the other hand, if you are in a very specific situation where you can assume that loop makes sense for all `k`, you can always `name.sub(/::\w+$/, '')` and `const_get`, modulus details. In a project, in a library, you may have constraints in place that you can exploit. In Ruby, the language, you don't.


----------------------------------------
Feature #17753: Add Module#namespace
https://bugs.ruby-lang.org/issues/17753#change-91475

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
----------------------------------------
Given code like this:

```ruby
module A
  module B
    class C; end
    class D; end
  end
end
```

We can get from `C` to `B` like `C.outer_scope`, or to `A` like
`C.outer_scope.outer_scope`.

I want to use this in cases where I don't know the outer scope, but I
want to find constants that are "siblings" of a constant.  For example,
I can do `A::B::C.outer_scope.constants` to find the list of "sibling"
constants to `C`.  I want to use this feature when walking objects and
introspecting.  For example:

```ruby
ObjectSpace.each_object(Class) do |k|
  p siblings: k.outer_scope.constants
end
```

I've attached a patch that implements this feature, and there is a pull request on GitHub [here](https://github.com/ruby/ruby/pull/4326).

---Files--------------------------------
0001-Add-Module-outer_scope.patch (5.93 KB)
0001-Add-Module-namespace.patch (5.89 KB)


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