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Date: Sun, 17 Aug 2014 22:59:05 +0100
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References: <235C617B-25E1-4185-A784-38EF1D7BFFDC@ajf.me> <CAFMT4NpziftUPjPQY9n9Qv5uA6-qV4_EkdTOk8=ZnK5JO19zoQ@mail.gmail.com>
To: Levi Morrison <levim@php.net>,
 Stas Malyshev <smalyshev@sugarcrm.com>
Subject: Re: [PHP-DEV] [VOTE][RFC] Closure::call()
From: ajf@ajf.me (Andrea Faulds)


On 17 Aug 2014, at 22:36, Levi Morrison <levim@php.net> wrote:

> I have a small clarification question on the RFC: you are adding
> another parameter to bindTo which defaults to false, but I didn't
> quite understand the reasoning. Can you try explaining that to me in a
> different way?

I=92ll give it a go.

Closures have a bound object and a scope. The bound object is whatever =
$this will be set to when that closure is called. The scope is the class =
whose private variables can be seen by a closure.

->call() will call the closure and use its existing scope but the bound =
object will be what is passed as its first parameter. ->call() doesn=92t =
permit calling with a different scope.

This presents a conundrum, however, if you want to use ->call() with a =
closure and you want to have a scope. Currently, ::bind() and ->bindTo() =
only permit two types of closures with scopes: those that are static =
(can=92t have $this bound) and those that have an object bound. This =
means to create a closure with a scope that you can then use with =
->call(), you=92d have to make one with a dummy object already bound. In =
most cases you can do this, but there are a few you can=92t, and it=92s =
weird to have to bind an object when we=92re not going to use it anyway =
as ->call() is going to override it.

For this reason, a third parameter is added to ::bind() and ->bindTo() =
which makes it produce an unbound, scoped closure rather than a static =
scoped closure if we don=92t pass an object to be bound and we specify a =
scope. The need for the third parameter is really just =
backwards-compatibility. At the moment, if you pass  NULL for the object =
to bind to and pass a class name for the scope, it=92ll make a static =
closure. We could change this and make it produce an unbound closure and =
add some other mechanism to obtain a static closure, but that would =
break backwards-compatibility. For this reason, we instead add a third =
parameter to say, yes, we do want an unbound closure. The same thing is =
done internally too, with zend_create_closure_ex.

On 17 Aug 2014, at 22:55, Stas Malyshev <smalyshev@sugarcrm.com> wrote:

> Hi!
>=20
>> I have a small clarification question on the RFC: you are adding
>> another parameter to bindTo which defaults to false, but I didn't
>> quite understand the reasoning. Can you try explaining that to me in =
a
>> different way?
>=20
> Interestingly enough, the RFC doesn't even mention this change.


It does, but maybe you missed it. Under the Proposal section:

> To solve this, we relax the current invariant of scoped closures =
having to be bound, and add a new parameter to bind(To) to produce an =
unbound, scoped closure, like so:

--
Andrea Faulds
http://ajf.me/