From: Sam Kong <sam.s.kong@...>
Date: 2007-08-17T06:04:58+09:00
Subject: Re: Lazy function definition pattern in Ruby?

On Aug 16, 1:18 pm, "Wolfgang N�dasi-Donner" <ed.oda...@wonado.de>
wrote:
> Sam Kong wrote:
> > Hi,
>
> > Yesterday, I read a blog about lazy function definition pattern in
> > JavaScript athttp://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
>
> You can define a method inside a method directly.
>
> class Bar
>   def foo
>     @t = Time.new
>     def foo
>       @t
>     end
>     @t
>   end
> end
>
> x=Bar.new
> p x.foo # => Thu Aug 16 22:17:17 +0200 2007
> sleep 5
> p x.foo # => Thu Aug 16 22:17:17 +0200 2007
>
> Wolfgang N�dasi-Donner
> --
> Posted viahttp://www.ruby-forum.com/.

I didn't know defining the same method in a method works.
It's very similar to the one David suggested above.
But the syntax is easier and more intuitive.
It's almost same as JavaScript's pattern.
It's good to know.^^

Thanks.