From: Michael Edgar <adgar@...>
Date: 2011-07-30T08:03:43+09:00
Subject: Re: avoiding capturing local variables in closures

On Jul 29, 2011, at 5:48 PM, Chuck Remes wrote:

> def some_callback(bigarg1, bigarg2)
>  foo = transform(bigarg1)
>  bar = transformagain(bigarg2)
> 
>  schedule_for_execution { baz(foo, bar) }
> end
> 
> If I am understanding things correctly, the block passed to #schedule_for_execution is capturing the variables foo, bar, bigarg1 and bigarg2. I could avoid capturing bigarg1 and bigarg2 with a small refactoring.
> 
> def some_callback(bigarg1, bigarg2)
>  foo = transform(bigarg1)
>  bar = transformagain(bigarg2)
> 
>  avoid_capture(foo, bar)
> end
> 
> def avoid_capture(foo, bar)
>  schedule_for_execution { baz(foo, bar) }
> end
> 
> Is this sufficient to avoid capturing those args in the closure? If not, what do I need to do?

That should be sufficient - there's no more reference to some_callback's
environment where bigarg1 and bigarg2 are referenced. Another
approach might be, on 1.9:

def some_callback(bigarg1)
  foo = transform(bigarg1)
  schedule_for_execution { |;bigarg1| bad(foo) }
end

This is the only real reason I know of for using the Ruby 1.9 block-local syntax. As
long as the implementation is smart enough not to foolishly store bigarg1.

Michael Edgar
adgar@carboni.ca
http://carboni.ca/