From: Russ McBride <russ@...>
Date: 2009-07-06T07:01:34+09:00
Subject: Re: to_proc and Proc/block conversion with &

Thanks.  Interesting discussion.

> given &expr, if expr is a Proc object, use it as
> the block; if not, call to_proc on it.
... and then use the resulting proc as a block.

Maybe the best way to think of & is a a proc/block converter, which,
if called on something that is neither looks first for a to_proc  
method before
performing its conversion.

The following seems quite surprising to me and I, too, would rather have
a warning I think than this default behavior.
    def f ; Proc.new ; end
    p = f { "hello" }
    p.call
      #=> "hello"


> Maybe it should be deprecated in practice. It's not apparent what's  
> going on, and rdoc can't pick it up (I presume?). It's usually  
> better to be more explicit using 'def foo(&b)' or yield.
>
> The only use I can think of for this feature[1] is if you want to  
> conditionally instantiate the Proc, as in:
>
>  def defer time
>    if time < Time.now
>      yield
>    else
>      pr = Proc.new
>      # store pr somewhere and schedule it for execution
>    end
>  end

But, you could just do something like this, right?

  def defer(time, &some_block)
    if time < Time.now
      yield   # or some_block.call
    else
      pr = some_block
      # store pr somewhere and schedule it for execution
    end
  end

Cheers,
Russ

P.S.  Joel, I seen now why you were inclined toward Rhodes.  :-)