[ruby-core:100996] [Ruby master Feature#17336] using refined: do ... end

Issue #17336 has been updated by k0kubun (Takashi Kokubun).


> Is it annoying in practice?

In practice? Nah, maybe not for many people, at least you. I admit I'm a bit extreme about indentation, and for sure it annoys *me*.

> It kind of seems nice to have the outer using do ... end which is saying "below are local monkey patches for this file".

For me, a word `refine` is enough to expect a monkey patch.

> I guess an example of real code where the deep indentation is problematic might help to convince me and maybe others.

While I would say it's not a problem for many people but me, here's the deepest indentation of `def` I've ever seen: https://github.com/rails/rails/blob/v6.0.3.4/activejob/lib/active_job/arguments.rb#L73-L96

----------------------------------------
Feature #17336: using refined: do ... end
https://bugs.ruby-lang.org/issues/17336#change-88663

* Author: k0kubun (Takashi Kokubun)
* Status: Closed
* Priority: Normal
----------------------------------------
## Problem
When we need a monkey patch which is used only in a single file, we'd like to define a refinement and use it in the same place. The problem is that it needs deep indentation and `Module.new { ... }` which feels redundant.

```rb
class Foo
  using Module.new {
    refine Array do
      def flat_map!(&block)
        replace(flat_map(&block))
      end
    end
  }
  
  # ...
end
```

@tagomoris proposed an idea to reduce indentation and remove `Module.new { ... }`. This looks pretty convenient, but I want to write `do ... end`, which would make it a block of `using` here, because we almost always use `... end` for defining methods or modules.

```rb
module Kernel
  def refined(mod, &block)
    Module.new do
      refine(mod, &block)
    end
  end
end

class Foo
  using refined(Array) {
    def flat_map!(&block)
      replace(flat_map(&block))
    end
  }

  # ...
end
```

## Proposal
How about supporting this? Because `using` currently doesn't take a block, it doesn't conflict with the existing syntax.

```rb
class Foo
  using refined: Array do
    def flat_map!(&block)
      replace(flat_map(&block))
    end
  end

  # ...
end
```

This syntax is based on ideas of @tagomoris and @znz .



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