[ruby-core:117939] [Ruby master Feature#20498] Negated method calls

20 May 2024

      Issue #20498 has been updated by hmdne (hmdne -).

I saw such a proposal before and I thought of some syntax and implementation, but I didn't submit that in the previous issue:

```ruby
class MethodNegator < BasicObject
  def initialize(obj)
    @obj = obj
  end

  def method_missing(method, ...)
    @obj.public_send(method, ...)
  end

  def respond_to_missing?(include_all = false)
    @obj.respond_to?(include_all)
  end
end

module Kernel
  def non(sym=nil)
    if sym
      proc { |*args,**kwargs,&block| !sym.to_proc.call(*args,**kwargs,&block) }
    else
      MethodNegator.new(self)
    end
  end
end

p "".non.empty?
# => true
p ["", "a", "b"].select(&non(:empty?))
# => ["a", "b"]
```

----------------------------------------
Feature #20498: Negated method calls
https://bugs.ruby-lang.org/issues/20498#change-108354

* Author: MaxLap (Maxime Lapointe)
* Status: Open
----------------------------------------
I want to propose the following syntax: `foo.!bar`. I know it's already valid syntax, but please read on for details.

When someone write a somewhat long line of code that is negated, the main way I've seen of doing it is:

```
must_create_user = !User.where(somelong: :condition, even_more: "thing").exists?
```

I personally highly dislike it, as I must keep the "not" in the back of my mind as I read the line. When quickly reading a line like this, it's super easy to misread and understand the opposite result.

The current ways around this I can think of are: 
* rename the variable (can be annoying)
* Use `unless` (only possible when in a condition; some people, like me, have a hard time grapsping a `unless`)
* use a `.!`in the end (`foo.exists?.!`), I've never seen that and it looks ugly to me (this is subjective).
* create a new method name with the negated meaning (not always possible)

My proposal would look like this:

```
must_create_user = User.where(somelong: :condition, even_more: "thing").!exists?
```

You cannot forget the bang that you saw 15 words ago, it's right there.

It also basically reads as English: "user where ... doesn't exists".

The main argument against this I can think of is that it's technically already a valid syntax. I believe it's frowned upon to override the bang operator and I'm not aware of places where it is overridden to with also having a parameter.

I made a prototype in RubyNext, which you can try here: https://ruby-next.github.io/#gist:0e133bf6f27f2437193dc034d58083dc

-- 
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