From: "David A. Black" <dblack@...>
Date: 2009-07-08T22:28:25+09:00
Subject: Re: Symbol#to_proc with arguments

Hi --

On Wed, 8 Jul 2009, James Coglan wrote:

> 2009/7/8 David A. Black <dblack@rubypal.com>
>
>> Hi --
>>
>>
>> On Wed, 8 Jul 2009, James Coglan wrote:
>>
>>> You could rewrite Symbol#to_proc to take arguments, and call #to_proc
>>> explicitly when calling #collect.
>>>
>>> class Symbol
>>>  def to_proc(*args)
>>>   lambda { |o| o.__send__(self, *args) }
>>>  end
>>> end
>>>
>>> %w[apple banana peach plum pear].collect &:split.to_proc('l')
>>> #=> [["app", "e"], ["banana"], ["peach"], ["p", "um"], ["pear"]]
>>>
>>
>> That's going to be incomprehensible, except by guesswork, to anyone
>> who doesn't know that you've modified Symbol. It also undoes whatever
>> benefit you might get from the &obj idiom automatically calling
>> #to_proc. I'd just do:
>>
>>  array.map {|e| e.split('l') }
>
>
> I wouldn't say it's incomprehensible since it maintains the existing
> semantics of Symbol#to_proc.

I don't think that's right. The existing semantics don't include any
arguments. So my reaction would be: isn't that going to raise an
exception? Then I'd have to figure out that you'd probably overridden
then method.

> The explicit block version is shorter though,
> and will likely perform better.
>
> No real reason to second-guess Ruby on this. If you really want to
>> modify Symbol, creating an entirely new method would probably be
>> better:
>>
>>  array.map(&:split.to_argument_accepting_proc('l'))
>
>
> The real problem here is that a Symbol contains a single piece of
> information, whereas we want to build a Proc from several pieces of
> information.

Just rename your override of #to_proc to #to_proc_with_args (or
whatever). It will still work the same. (You're dispensing with the
automatic calling of #to_proc anyway.)

> So, an alternative:
>
> class Array
>  def to_proc
>    lambda { |o| o.__send__(first, *self[1..-1]) }

That doesn't differ from __send__(*self), does it?


David

-- 
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