Project

General

Profile

Feature #7914

Case for local class methods

Added by trans (Thomas Sawyer) over 7 years ago. Updated over 2 years ago.

Status:
Open
Priority:
Normal
Target version:
-
[ruby-core:52701]

Description

=begin
Here is a use case for local class methods.

Say we wish to give certain classes and all subclasses a special name.

class X
def self.special_name
"special:#{name}"
end
end
class Y < X; end
class Z < Y; end

Z.special_name #=> "special:Z"

But what if Y has a unique special name?

class Y < X
def special_name
'unique:Y'
end
end

Problem that arises:

Z.special_name  #=> "unique:Y"  # wrong!

Currently, to solve this would require creating an additional method, e.g. unique_name and redefine special_name to first look for unique_name then fallback to default special name if non-found. It works, but adds additional complexity to API.

Nicer solution would be local class methods.

class Y < X
  def special_name
    'unique:Y'
  end
  local :special_name
end

Y.special_name  #=> "unique:Y"
Z.special_name  #=> "special:Z"

The idea being that local class methods are skipped in super/lookup chain.

This idea is not without precedence. Module class methods can be thought of as being local. So this idea has other side of the notion, that modules could have class methods that are not skipped over in the super/lookup chain. In that case we would need a term that means opposite of local, so I'll use nonlocal:

module M
  def self.q; "q"; end
  nonlocal :q
end

class X
  include M
end

X.q  #=> "q"

=end

Also available in: Atom PDF