[ruby-core:123130] [Ruby Feature#21555] Add support for predicate attribute reader names

["shan (Shannon Skipper) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #21555 has been updated by shan (Shannon Skipper).


Dan0042 (Daniel DeLorme) wrote in #note-2:
> Also related to #5781 #11167 #12046 #15991 #19708
> Popular eh?

Wow! There's already an open ticket for this exact issue even. I apologize for not properly searching before filing. I should have just added a PR link there in retrospect.

byroot (Jean Boussier) wrote in #note-3:
> > This feature is only supported for attr_reader and attr, not attr_writer or attr_accessor, since setter methods cannot have question marks.
> 
> Using the same logic, `attr_accessor :enabled?` could generate `#enabled?` and `#enabled=` without problem. `attr_writer :enabled?` would be weird though.

I was thinking of `attr_writer :enabled?` being weird and dismissed `attr_accessor :enabled?`. I didn't think of the case where you want `attr_reader :enabled?` and `attr_writer :enabled` without `attr_writer :enabled`. I wouldn't mind doing an `attr_reader :enabled?` with `attr_writer :enabled` but agree `attr_accessor :enabled?` makes sense based on the pattern.

----------------------------------------
Feature #21555: Add support for predicate attribute reader names
https://bugs.ruby-lang.org/issues/21555#change-114457

* Author: shan (Shannon Skipper)
* Status: Open
----------------------------------------
After manually aliasing predicate methods many times, I wanted to propose letting `attr_reader` take predicate method names that correspond to instance variables of the base name without a trailing question mark. https://github.com/ruby/ruby/pull/14391

If the base name method doesn't already exist, a predicate name defines a base name method attribute reader to alias then undefines the base name.

For example, this creates an `enabled?` method that reads `@enabled`:
```ruby
attr_reader :enabled?
```

This feature is only supported for `attr_reader` and `attr`, not `attr_writer` or `attr_accessor`, since setter methods cannot have question marks.

Example:
```ruby
class Example
  attr_reader :valid?, :meaning

  def initialize
    @valid = [true, false].sample
    @meaning = 42
  end
end

Example.new.valid? #=> true
```



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