From: Sam Kong <sam.s.kong@...>
Date: 2007-08-17T02:59:59+09:00
Subject: Lazy function definition pattern in Ruby?

Hi,

Yesterday, I read a blog about lazy function definition pattern in
JavaScript at http://peter.michaux.ca/article/3556 .
It was interesting and insightful.

<snip>
Write a function foo that returns a Date object that holds the time
that foo was first called.

var foo = function() {
    var t = new Date();
    foo = function() {
        return t;
    };
    return foo();
};
</snip>

In ruby, one would write the following way or something like that if
he wants to cache the first value.

def foo
  @t or (@t = Time.new)
end

But the writer wants to remove the conditional part because it's run
every time the function is called.
JavaScript allows functions to be redefined very easily.
I think ruby allows it but not very easily.

I came up with this idea.

class Lazy
  def method_missing *args
    if args[0] == :foo
      @t = Time.new
      class << self
        def foo
          @t
        end
      end
      return foo
    end
  end
end

But I believe that ruby gurus will have better ideas.
What would be the lazy function definition pattern in ruby?
And do you think it's useful?

Thanks in advance.

Sam