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Subject: Re: [PHP-DEV] On closures and lamdba
From: ionut.g.stan@gmail.com ("Ionut G. Stan")



On 2/24/10 8:56 AM, Stanislav Malyshev wrote:
> Hi!
>
>> Correct me if I'm wrong, but given the fact that PHP only* supports
>> functions defined in the global space**, with the additional ability to
>> import global variables using the global statement, wouldn't that make
>> named functions able to close-over global variables?
>
> It's different mechanism. Globals are just references to variables in
> same global scope, they are not bound to any function, etc.
>
>> And, if the above is true, wouldn't it be consistent to support the use
>> statement on named functions, and then deprecate the global statement?
>
> That's why I'm not a big fan of that "consistency" argument here on the
> list - because it usually means "let's implement some feature because I
> like it", but not more. Which is fine, but it has nothing to do with
> consistency.
> Particularly, scope capturing and all that has very little relation to
> what globals do. Closures carry around "captured" variables. Regular
> functions don't. Global scope exists independently of them.
> The mechanism is similar (well, it's the same engine, how many there can
> be? :) but they are not the same.

What I was thinking when writing my previous email was this:

1. Named functions using global variables (both can read and modify the 
global variable):

$global_var = 'foo';

function named_1() {
     global $global_var;
}

function named_2() {
     global $global_var;
}



2. Closures (both lambdas can read and modify the local var)


list($closure_1, $closure_2) = call_user_func(function () {

     $local_var = 'foo';

     return array(
         function () use(& $local_var) {},
         function () use(& $local_var) {},
     );
});


As I see it right now, there's a duplication of concepts in there. The 
only difference is that the first example uses the global scope, while 
the second one uses the scope of an anonymous function.

But I admit this is just a nice-to-have thingy, not a necessity. Well, 
for me at least. So I won't ask for it anymore :).


>
>> ** namespaced functions don't make any difference, as variables aren't
>> namespaced.
>
> I'm not sure what you mean here, as variables in PHP are scoped. Global
> functions are not scoped, of course, but can be namespaced.

I mean that variables declated outside of a namespaced function or class 
are not namespaced.

namespace foo;

$this_is_a_global_var = 'foo';

function namespaced_function() {
     global $this_is_a_globa_var;
}


-- 
Ionut G. Stan
I'm under construction  |  http://blog.igstan.ro/