[ruby-core:112773] [Ruby master Feature#19521] Support for `Module#name=` and `Class#name=`.

Issue #19521 has been reported by ioquatix (Samuel Williams).

----------------------------------------
Feature #19521: Support for `Module#name=` and `Class#name=`.
https://bugs.ruby-lang.org/issues/19521

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
----------------------------------------
See https://bugs.ruby-lang.org/issues/19450 for previous discussion and motivation.

This proposal introduces `Class#name=` to set the temporary class name. This is an alternative or addition to <https://bugs.ruby-lang.org/issues/19520>.

```ruby
c = Class.new do
  self.name = "fake name"
end

c = Class.new
c.name = "fake name"
```

Alternatively, we could use `set_name`:

```ruby
Class.new do
  set_name "fake_name"
end
```

## Example usage

The current Ruby test suite has code which shows the usefulness of this new method:

```ruby
  def labeled_module(name, &block)
    Module.new do
      singleton_class.class_eval {
        define_method(:to_s) {name}
        alias inspect to_s
        alias name to_s
      }
      class_eval(&block) if block
    end
  end
  module_function :labeled_module

  def labeled_class(name, superclass = Object, &block)
    Class.new(superclass) do
      singleton_class.class_eval {
        define_method(:to_s) {name}
        alias inspect to_s
        alias name to_s
      }
      class_eval(&block) if block
    end
  end
  module_function :labeled_class
```

The updated code would look like this:

```ruby
  def labeled_module(name, &block)
    Module.new do
      self.name = name
      class_eval(&block) if block
    end
  end

  def labeled_class(name, superclass = Object, &block)
    Class.new(superclass) do
      self.name = name
      class_eval(&block) if block
    end
  end
  module_function :labeled_class
```

Because the name cannot be set as part of `.new`, we have to have a separate block to set the name, before calling `class_eval`. I think the ergonomics and performance of this are slightly worse than the [counter proposal](https://bugs.ruby-lang.org/issues/19520).



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