From: mame@...
Date: 2020-12-23T15:25:57+00:00
Subject: [ruby-core:101649] [Ruby master Feature#17314] Provide a way to declare visibility of attributes defined by attr* methods in a single expression

Issue #17314 has been updated by mame (Yusuke Endoh).


Hi, I've just noticed that this changeset allows not only `Module#private` but also `Module#private_class_method` to accept an array of symbols. `Module#public_class_method` too.

```
class Foo
  def self.foo; end
  def self.bar; end  
  private_class_method [:foo, :bar] # No error
end
```

And toplevel `Kernel#private` and `Kernel#public` do too.

```
def foo = nil
def bar = nil

private [:foo, :bar]
public [:foo, :bar]
```

I cannot think of a case where we want to pass an array of symbols to `public_class_method` and toplevel `public`. (Note that there is no toplevel `attr_reader`.) So I believe these changes are not intentional. But it may be more consistent for the methods to allow a symbol array. I have no opinion whether the additional methods should allow or deny an array. What do you think?

Anyway, I've added a rdoc, tests, and NEWS for the extra methods at 3a81daaf8dc037057d96b8e8cdc6ab1691e7e9d9.

----------------------------------------
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-89439

* Author: radarek (Rados��aw Bu��at)
* 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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