From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-05-06T17:40:04+09:00
Subject: Re: for-in vs. map closures

On Wed, May 5, 2010 at 11:50 PM, Mike Austin <mike_ekim@yahoo.com> wrote:
> 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.

I suppose it's slower but I think it's mainly because the block call.
Let us know if you test it.

Jesus.