[ruby-core:104339] [Ruby master Bug#11779] Module#using does not make sense as a method

Issue #11779 has been updated by Eregon (Benoit Daloze).


`Module#using` has a granularity of "constant lexical scope", i.e., a scope that is only changed by `module` or `class` keywords.

Maybe the docs should be improved in this regard?

Current docs say this
```
Import class refinements from module into the current class
or module definition.
```
which seem fair enough but could be more precise (i.e., only for `module` or `class` keywords, not for module_eval/module_exec/etc).

----------------------------------------
Bug #11779: Module#using does not make sense as a method
https://bugs.ruby-lang.org/issues/11779#change-92562

* Author: bughit (bug hit)
* Status: Feedback
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* ruby -v: 2.2.3
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
1. it can't be called from another method
2. the receiver must be self
3. since refinements are lexically scoped the self receiver must match the currently open class

#3 is particularly curious

```ruby
module Refinement
  refine String do
    def refined?
      true
    end
  end
end

module Foo
  def self.refined?
    ''.refined? rescue false
  end
end


module Bar
  def self.refined?
    ''.refined? rescue false
  end
  Foo.module_eval do
    using Refinement

  end
end

p Foo.refined? #false
```

The module_eval `#using` call does not raise (it's not from a method and the receiver is self), but evidently because currently open class does not match self, it does not do anything. So it should at least raise.

So `#using`, though a method, does not function as a method, which is misleading.



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