From: Mike Austin <mike_ekim@...>
Date: 2010-05-06T06:50:08+09:00
Subject: Re: for-in vs. map closures

On May 5, 9:01 am, Jesús Gabriel y Galán <jgabrielyga...@gmail.com>
wrote:
> On Wed, May 5, 2010 at 5:45 PM, Josh Cheek <josh.ch...@gmail.com> wrote:
> > Wow, those were both really good explanations. Thanks David and Jesus.
>
> In fact there was something not so clear (or just plain wrong,
> depending who you ask :-), in my explanation. I said:
>
> > Here n is the same in all iterations (it's outside the do ... end),
> > for defines it in the scope that is above the block
>
> The fact that n is outside the do...end has nothing to do with the
> rest of the explanation. As David said, for doesn't start a new scope,
> so even if it were like this it wouldn't yield different results:
>
> irb(main):008:0> a = []
> => []
> irb(main):009:0> for i in [1,2] do
> irb(main):010:1> value = i
> irb(main):011:1> a << lambda {value * value}
> irb(main):012:1> end
> => [1, 2]
> irb(main):013:0> a.each {|l| puts l.call}
> 4
> 4
>
> Even though value is inside the block, as the for keyword doesn't
> create a new scope, value is defined in the outer scope. So, what's
> here between the do...end is not a regular ruby block, in fact, the do
> is optional:
>
> irb(main):008:0> a = []
> => []
> irb(main):009:0> for i in [1,2]
> irb(main):010:1> value = i
> irb(main):011:1> a << lambda {value * value}
> irb(main):012:1> end
> => [1, 2]
> irb(main):013:0> a.each {|l| puts l.call}
> 4
> 4
>
> After either of those:
>
> irb(main):020:0> defined? value
> => "local-variable"
>
> Jesus.

So if a new context is created for every block call in map(), in
theory it should be slower than a for-in loop, correct?  I'll have to
try it when I get home.

Mike