From: Paul Brannan <pbrannan@...>
Date: 2001-08-25T01:42:06+09:00
Subject: [ruby-talk:20302] Re: another new toy

On Sat, 25 Aug 2001, ts wrote:

> ./b.rb:6:in `new': can't use new for this class (RuntimeError)
>         from ./b.rb:24
> pigeon%
>
>
>  I've not yet found an use for this stupid toy :-)))
>
>
> Guy Decoux


Well, one use would be so that you could have a class that only has static
functions, but cannot be mixed in (since it is a Class and not a Module).
This (arguably) gives you a slightly safer form of namespace.

Another use would be to "hide" the fact that a particular class can be
instantiated; instead of raising an exception in all cases, only raise an
exception when the caller passes a binding as an argument that does not
match an authorized "friend" class:

class Foo
  private_class_method :new

  def self.create(b, *args)
    other = eval("self", b)
    raise "Unauthorized access to create" if not Bar === other
    return new(*args)
  end

  def foo
    return "foo"
  end
end

class Bar
  def bar
    puts Foo.create(binding).foo
  end
end

b = Bar.new
b.bar
puts Foo.create(binding).foo

This produces:

foo
friend.rb:6:in `create': Unauthorized access to create (RuntimeError)
        from friend.rb:23

And could be a mixin just as you suggested before.

Paul