From: dblack@...
Date: 2006-03-16T05:57:36+09:00
Subject: Re: executing a block in the context of receiver

Hi --

On Wed, 15 Mar 2006, Ross Bamford wrote:

> On Wed, 2006-03-15 at 00:20 +0900, Mark Volkmann wrote:
>> In the following code the do_this instance method of the foo object
>> calls yield to run the block that is passed to it.
>>
>> foo.do_this(p1, p2) {
>>   do_that(p3, p4)
>> }
>>
>> Is there any way to make it so that do_that is executed in the context
>> of the foo object, i.e. it acts as though it was invoked with
>> foo.do_that(p3, p4)?  I know I could just say "foo.do_that(p3, p4)",
>> but I was wondering if I could avoid that.
>
> If you're writing 'foo' then you can do:
>
> 	class Foo
> 	  def do_this(&blk)
> 	    instance_eval &blk
> 	  end
>
> 	  def do_that
> 	    puts "Doing that..."
> 	  end
> 	end
>
> 	f.do_this { do_that }
> 	# (prints) Doing that...
>
> 	# can use this form, too
> 	f.do_this { |foo| foo.do_that }
> 	# (prints) Doing that...

But only if you yield self from do_this (just to clarify).  And
initialize f, but I guess that was implied :-)

I like the second form better.  Just having self change mysteriously
for the duration of a block always strikes me as a bit of an
obfuscation.


David

-- 
David A. Black (dblack@wobblini.net)
Ruby Power and Light, LLC (http://www.rubypowerandlight.com)

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