Re: I thought this was the one that worked?

"Chad Perrin" <[e-mail]> wrote in message 
news:[e-mail]...
> On Tue, Aug 01, 2006 at 10:15:09AM +0900, Just Another Victim of the 
> Ambient Morality wrote:
>>
>> "Chad Perrin" <[e-mail]> wrote in message
>> news:[e-mail]...
>> >
>> > Who said it's different?  I'm just asking about the foregoing statement
>> > that all blocks are closures (which strikes me as improbable).  That's
>> > like saying that this will generate a closure (which it won't):
>> >
>> > sub foo {
>> >  return sub { my $bar = 1; print ++$bar };
>> > }
>>
>>     Okay, the mere fact that you "used a Perl example" demonstrates that
>> there is a miscommunication going on here.  Why would an example from 
>> Perl
>> clear anything up?  It's a different language with different semantics. 
>> Are
>> you hoping that we all know Perl?
>
> I'm hoping that demonstrating how it does or does not work in Perl will
> make it clear what I'm talking about, based on similar syntax between
> the languages, so that I can find out what does and does not work in
> Ruby.  Duh?

    Well, I suppose the question can be directed only to those who know Perl 
but the two languages seem to be sufficiently different (despite Ruby's Perl 
origins) that your analogies are hard to make or make clear...


>>     I suspect what's happening here is that we're mixing up code blocks 
>> with
>> "Ruby blocks."
>>     These are examples of what most programmers would call blocks but are
>> _not_ Ruby blocks:
>
> I know there's a difference, thanks.  The problem is that nobody seems
> to be addressing the fact that for a proper closure, as I understand it,
> the closure variable has to go out of scope while the block of code does
> not.  If Ruby blocks do something automagical to make variables declared
> within them go out of scope while the block is still in scope, I'd like
> to know.  If there's some other way to "close" the block's data while
> the block is still available, I'd like to know that, too.

    I'm having trouble parsing your sentences here so I am going to pretend 
that I understand you and you can tell me where I'm going wrong, okay?


>> def some_method_as_function
>>     # code block goes here but
>>     # in the Ruby world, this is not a "block..."
>> end
>>
>> while some_condition
>>     # code block goes here but
>>     # in the Ruby world, this is not a "block..."
>> end
>>
>>
>>     These are Ruby blocks:
>>
>>
>> [1, 2, 3].each do |i|
>>     # this is a Ruby block and
>>     # this is a closure
>> end
>
> So explain how it is a closure.  Please.

    Okay, I think I can do this much...

    I'm going to implement the "each" method of an array using the passed in 
block, which is a closure, using the array reference operator "[]" and the 
size method...


local_variable = 2

class Array
    # local_variable is outside this scope..

    def each
        # local_variable is also outside this scope...

        i = 0
        while i < self.size

            # call the passed in block which is also a closure...
            yeild self[i]

            i += 1
        end
    end
end

array = [1, 2, 3]

array.each do |i|
    # we have access to local_variable even though this
    # will be executed far away from local_variable's scope
    # because this block of code is a closure...

    puts local_variable * i
end


>> some_local_variable = 2
>> func = lambda { puts some_local_variable }  # a one line block and 
>> closure
>
> Am I to assume that some_local_variable is going out of scope outside of
> the lambda declaration at some point, to create that closure?

    Yes, you are.  It didn't occur to me to demonstrate that it was a 
closure, only how to make blocks that are closures in Ruby.  I hope the 
previous paragraph demonstrated what you wanted to know...


>>     All things that are called "blocks" in Ruby are closures.
>>     Do you still have any questions on the matter?
>
> Yes.  Are you just failing to explain how these things are closures, or
> do you not know what a closure is?  You keep telling me blocks are
> closures somehow, but you're not explaining how.  Saying it doesn't make
> it so.  Please explain what I'm missing.

    I _think_ I know what a closure is, as long as Wikipedia and all Ruby 
tutorials haven't conspired to lie to me.  Again, it didn't occur to me show 
you that they are closures.  I was only trying to show you what will make a 
closure...
    So, are these closures, as you understand them?  How is your 
understanding different from mine?