From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2013-04-13T05:27:53+09:00
Subject: [ruby-core:54244] [ruby-trunk - Feature #7149][Open] Constant magic for everyone.


Issue #7149 has been updated by marcandre (Marc-Andre Lafortune).

Category set to core
Status changed from Feedback to Open
Assignee set to matz (Yukihiro Matsumoto)

I've never needed this, but I could envision a `const_assigned` callback. Whenever a constant is assigned to an object, then object.const_assigned("FullyQualified::Name") would be called.

In other words, the "magic" around Modules and Classes could be understood with the "equivalent" Ruby code:

    class Module
      def const_assigned(name)
        @name ||= name
      end

      def to_s
        @name || "#<Class:#{object_id}>"
      end
    end

I would guess that the runtime impact would be completely negligible.

In the examples given above, ChemicalSpecies could have a similar method. And yes, even (6*7).name could be "Foo::Bar" with:

    class Fixnum
      @@reg = {}
      def name
        @@reg[self] || to_s
      end
      def const_assigned(name)
        @@reg[self] ||= name
      end
    end
 
> What do you expect if the object is assigned to two or more constants?

That would be entirely up to the implementer of `const_assigned`, but `const_assigned` would be called multiple times.

----------------------------------------
Feature #7149: Constant magic for everyone.
https://bugs.ruby-lang.org/issues/7149#change-38508

Author: boris_stitnicky (Boris Stitnicky)
Status: Open
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: next minor


I noticed that certain objects have constant magic: When they are first assigned to a constant, they acquire a name property equal to the constant name string. I only know about Class and Struct objects behaving this way. I like this behavior, because I like to be able to say something like:

Adenosine = ChemicalSpecies.new initial_concentration: 5.micromolar
Adenosine.name #=> "Adenosine"

I like it so much, that I wrote a library (I call it ConstantMagicErsatz) for myself that searches whole namespace for the new objects assigned to constants. But searching whole wild namespace has its pitfalls. It is a wildly difficult workaround to get the candy I want. I am dreaming about just being able to say:

class ChemicalSpecies
  constant_magic true
end

and imbue ChemicalSpecies with the same constant magic ability that Class and Struct classes have. Could it be made possible, please?


-- 
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