From: "David A. Black" <dblack@...>
Date: 2009-07-05T21:41:03+09:00
Subject: Re: to_proc and Proc/block conversion with &

On Sun, 5 Jul 2009, David A. Black wrote:

> Hi --
>
> On Sun, 5 Jul 2009, Robert Dober wrote:
>
>> On 7/5/09, David A. Black <dblack@rubypal.com> wrote:
>>> Yes; the & means: take what's to the right of it (which can be any
>>> expression), evaluate it, call to_proc on the resulting object, and
>>> use the return value of to_proc to play the code block role.
>>> 
>>> In the case of a lambda, to_proc just returns the receiver. So you can
>>> do:
>>>
>>>    array.map &lambda {|x| x * 10 }
>> It might be interesting to note that in Ruby1.9 the to_proc is not
>> called on Proc objects, I wonder what happened in 1.8
>
> I guess it's an optimization. So take my explanation as behavioral
> rather than implementation-faithful.

Also, it seems to be the same in 1.8. So I guess a refinement of the
description would be: given &expr, if expr is a Proc object, use it as
the block; if not, call to_proc on it.

I don't know whether that's a language spec or just an implementation
detail. I vaguely hope the latter, though I suppose that something
like this:

   func = lambda {|x| x * 10 }
   def func.to_proc
     # some other proc
   end

would be extremely rare....


David

-- 
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