From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-05-06T01:01:24+09:00
Subject: Re: for-in vs. map closures

On Wed, May 5, 2010 at 5:45 PM, Josh Cheek <josh.cheek@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.