From: Kenichi Komiya <kom@...1.accsnet.ne.jp>
Date: 2001-07-20T11:06:12+09:00
Subject: [ruby-talk:18160] Re: Opaque constants? (in C?)


Hi,

From: Emil Ong <onge@mcs.anl.gov>
Subject: [ruby-talk:18150] Opaque constants? (in C?)
Date: Fri, 20 Jul 2001 07:16:35 +0900

> Is it possible to define opaque constants in ruby similar to true and
> false?  That is, if you were using irb and you wanted the value of the
> constant 'my_const', you would get something like this:

You can make an object 'opaque' by defining "inspect" as a
singleton method, so that it always returns "it's name".  

So, if you can live with captalized constant...

  irb(main):001:0> MY_CONST = Object.new
  #<Object:0x4028bfb8>
  irb(main):002:0> MY_CONST
  #<Object:0x4028bfb8>
  irb(main):003:0> def MY_CONST.inspect; "MY_CONST".freeze; end
  nil
  irb(main):004:0> MY_CONST
  MY_CONST

You can chose to define a uncapitalized pseudo constant (a
method always return the same object).

  class Object
    obj = Object.new
    define_method(:my_const) { obj }
  end
  def my_const.inspect
    "my_const".freeze
  end

In many situations, it works as if it is constant.  But, using
non-standard naming convention like this decrease readability,
IMHO.

> Moreover, can I do it from C?

MY_CONST version in C.

  VALUE my_const = rb_obj_alloc(rb_cObject);
  rb_define_singleton_method(my_const, "to_s", my_const_to_s, 0);
  rb_define_global_const("MY_CONST", my_const);

Best Regards,
Kenichi Komiya.