[ruby-core:113766] [Ruby master Feature#19708] Support `attr_reader :foo?`

Issue #19708 has been updated by Eregon (Benoit Daloze).


Agreed this would be nice and make such query methods more optimized.

In https://bugs.ruby-lang.org/issues/12046#note-3 it sounds to me matz was looking for a concrete use case, I think there are plenty in the wild.

I think a PR/patch for this would help to make progress (it might not be trivial).

----------------------------------------
Feature #19708: Support `attr_reader :foo?`
https://bugs.ruby-lang.org/issues/19708#change-103416

* Author: AMomchilov (Alexander Momchilov)
* Status: Open
* Priority: Normal
----------------------------------------
Creating reader methods with `attr_reader` is preferable over defining them by hand, not only because it's more convenient, but also because it hits a fast path in MRI (see `VM_METHOD_TYPE_IVAR`).

Since local and instance variables can't end with `?`, you can't use `attr_reader` to define predicate-style methods for boolean values, like:

```ruby
class Person
  attr_reader :name, :age, :active? # invalid attribute name `active?' (NameError)
  
  def initialize
    @name = "Bob"
    @age = 30
    @active = true
  end
end
```

It would be nice if `attr_reader` (and friends) could behave like:

```ruby
def active? = @active
```

(`attr_writer` and `attr_accessor` couldn't do the same, since `def active?=(new_value)` isn't valid, so they'd probably stick with `def active=(new_value)`)



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