closures questions View as Markdown

Hi Lukas,

1. Closures on class properties just don't work, the only way to do it is
   to do something like:

$c = $a->b;
$c();

Calling: $a->b(); will result in method A::B() does not exists.

Yes, that's expected behaviour (we had a few comments on this on the
list). Compare this to, for example:

function hello () { echo "Hello World!\n"; }
$a->b = 'hello';
$c = $a->b;
$a->b (); // undefined method
$c (); // works

But, as closures implement the __invoke method, it's possible to do
this:

$a->b->__invoke ();

or, of course

call_user_func ($a->b);

(which works with all types of callbacks, even non-closures)

so do we even want the toString() method?

Personally, I don't care.

4. var_export() and Closures is useless

What would you suggest? Having var_export return the function body for
the closures? But what about bound variables? Well, perhaps in the
future you could even export all the bound variables. But for know to
keep it simple I'd say it's best that closures can't be exported.

5. Its impossible to clone a closure using the cloning keyword:

$a = function(){};
$b = clone $a;

That's intended behaviour. What would be the clone of a closure?
Especially with bound variables? This would allow for all sorts of weird
behaviour.

Take, for example, the following:

class Foo {
private $someProperty;

function getPrinter ($outputDevice) {
return function ($text) use ($outputDevice) {
$outputDevice->print ($this->someProperty, $text);
};
}
}

How would you clone that? There are two bound variables in this closure:
$this and $outputDevice. Do you clone them both? Do you clone only
$this? Do you clone only $outputDevice? If you only clone the closure
object itself, it won't change the behaviour from simply creating
another reference to it...

If one really needs a clonable and callable object, write a class
that implements __clone and __invoke. Then the programmer can control
the exact semantics. Everything else would simply be extremely confusing.

And, if I take another language such as Python for example, there you
can't clone closures either, y = copy.deepcopy (closure) returns the
same object.

This makes it hard to make a copy of the closure because of objects
always are
passed by reference.

I guess this is a draw back from the OO approach (rather than the
original resource approach), but solvable?

No, the original resource approach was just the same. A resource is
basically an integer value which is then used to look up some specific
data. You can't clone a resource either.

Regards,
Christian

Hi!

so do we even want the toString() method?

IMHO we should drop toString from Closure.

Maybe it could return some relevant information for exporting the
closure across
data

not a huge biggy to me.

I don't think Closure can be meaningfully exported. Can we prohibit it?

I guess this is a draw back from the OO approach (rather than the
original resource approach), but solvable?

I think we can make working clone there - just copy all data, etc.

Stanislav Malyshev, Zend Software Architect
stas@zend.com http://www.zend.com/
(408)253-8829 MSN: stas@zend.com