From: mental@...
Date: 2006-02-20T11:43:50+09:00
Subject: Re: lazy.rb 0.9.5 -- transparent futures!

Quoting "matt.smillie@gmail.com" <matt.smillie@gmail.com>:

> If you suspected "the right thing" you'd probably be right:
>
> irb(main):001:0> require 'lazy'
> irb(main):002:0> x = promise { 5 + 3 }
> => #<Lazy::Promise computation=#<Proc:0x0035788c@(irb):2>>
> irb(main):003:0> p 3 * x
> 24
> => nil

It's worth noting that this only works so well because of the very
nice coercion machinery Ruby has built around its numeric classes.

Ruby's NUM2INT (for example) will call .to_int on the promise when
FIXNUM_P fails, so everything Just Works(tm).

For other cases (e.g. promises returning file handles), you may find
you need to unwrap them explicitly with demand() to pass them to
certain methods.

Of course this is an issue only when passing promises to methods
implemented in C; lazy.rb does a very good job of faking out Ruby
otherwise (the boolean issue notwithstanding).

-mental