Issue #17314 has been updated by zverok (Victor Shepelev).


> I cannot think of a case where we want to pass an array of symbols to `public_class_method`

Generally, there could be other DSLs that will define methods. Rails have [`mattr_{reader,writer,accesor}`](https://api.rubyonrails.org/classes/Module.html#method-i-mattr_accessor) (for **m**odule attributes), which currently does not return the "proper" value to pass to `public_class_method`, but they can be change to do so. Then, this would make sense:

```ruby
class A
  private_class_method mattr_reader :some, :internals
end
```

----------------------------------------
Feature #17314: Provide a way to declare visibility of attributes defined by attr* methods in a single expression
https://bugs.ruby-lang.org/issues/17314#change-89446

* Author: radarek (Radosaw Buat)
* Status: Closed
* Priority: Normal
----------------------------------------
**Description**

Many of us (me included) declare class attributes, even if they are private, on the top of class definition. When reading source code it's convinient to see what kind of attributes class has.

To declare private attributes we can:
* declare them with one of `attr*` methods and later change visiblity calling `private`
* call `private` without argument, then declare attributes and finally call (in most cases) `public` to keep defining public methods
* declare attribute on top of the class but make them private in private section later in a file

``` ruby
clsss Foo
  attr_accessor :foo
  private :foo, :foo= # we have to remember about :foo= too

  private

  attr_accessor :bar

  public

  # rest of the code
end
```

To simplify it and create other possibilites I propose to:
* change `attr*` methods so as they return array of defined methods names
* allow `public/protected/private` methods to receive array of methods names (single argument)

With requested feature we could write code like this:

``` ruby
class Foo
  private attr_accessor :foo, :bar
end
```

Additionaly you could use `attr*` with your own methods. Something like this:

``` ruby
class Module
  def traceable(names)
    # ...
    names
  end
end

class Foo
  traceable attr_accessor :foo
  # it can be mixed with public/protected/private too
  protected traceable attr_accessor :bar
end
```

**Backward compatibility**

* `attr*` methods currently return `nil` so there should be no problem with changing them
* `public/protected/private` methods receive multiple positional arguments and convert all non symbol/string objects to strings. I can imagine only one case where compatibility would be broken:

``` ruby
class Foo
  def foo; end
  def bar; end

  arr = [:foo]
  def arr.to_str
    'bar'
  end

  private arr
end

p [Foo.public_instance_methods(false), Foo.private_instance_methods(false)]
```

Currently `[[:foo], [:bar]]` would be displayed, `[[:bar], [:foo]]` after requested feature is implemented.

**Implementation**

You can view my implementation in this (draft) PR: https://github.com/ruby/ruby/pull/3757




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