From: "David A. Black" <dblack@...>
Date: 2007-10-15T01:29:29+09:00
Subject: Re: Parameter in a block is not local?

Hi --

On Sun, 14 Oct 2007, SpringFlowers AutumnMoon wrote:

> I thought a iterator with a block is like an nameless function call...
> so if it is a function call, the parameter is local.
> but for the following, the output is surprising:
>
> a = 1
> p a
>
> 1.upto(10) {|a| p a}
>
> p a
>
> --------------
>
> E:\>ruby test_iterator.rb
> 1
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9
> 10
> 10
>
> a is changed!
>
> but is it true that the "a" is not global to begin with....
> but then, isn't the "a" inside the block more local than the "a"
> outside?

a is local, not global. The semantics of block parameters is
assignment semantics:

   |a|

basically means "a = ...", in the same scope as the scope in which the
block is created. Blocks are different in that respect from methods,
and the || notation (instead of (), as in methods) is a good reminder
that they're not the same. (Not that || specifically implies
assignment semantics, but it's a reminder that there's a difference.)


David

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