From: Rick DeNatale <rick.denatale@...>
Date: 2007-10-16T03:47:47+09:00
Subject: Re: Parameter in a block is not local?

On 10/15/07, 7stud -- <bbxx789_05ss@yahoo.com> wrote:
> SpringFlowers AutumnMoon wrote:
> >
> > I thought a iterator with a block is like an nameless function call...
> >
>
> Here's another example(a modification of the example found  in pickaxe2,
> p 106):
>
> if false
>   data = "hello"
> end
>
> (1..3).each {data = "goodbye"}
>
> puts data
>
> --output:--
> goodbye
>
>
> That is equivalent to Java's call by value--but using references and C++
> reference semantics, and the flat scope is converted to spheric scope
> with assignment semantics applying throughout any call by value passing.

No it's not. no matter what 'spheric scope' means.

Blocks are closures, they are NOT functions/methods.

In the example the variable 'data' in the block is the same variable
as 'data' in  data = 'hello'

In that sense this is no different than

if false; data = 'hello';end
data = 'goodbye'

The variable definition is lexical, so it doesn't matter that the
data='hello' statement didn't get executed, it's the fact that the
parser saw it which caused it to be defined.

And note that if you JUST had

1.times {a = "goodbye"}

with no prior definition of a in the scope, you'd get a NameError when
you ran it because a is undefined, and Ruby 1.8 doesn't allow new
locals to be defined within a block.

Ruby 1.9 has a feature marked EXPERIMENTAL which allows block locals
to be defined by listing them in the |'s preceded by a ; after any
block arguments.  This might or might not survive.

-- 
Rick DeNatale

My blog on Ruby
http://talklikeaduck.denhaven2.com/