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To: Nikita <inefedor@gmail.com>
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Subject: Re: [PHP-DEV] Generics proposal
From: jpauli@php.net (jpauli)

On Sat, Oct 20, 2012 at 10:59 PM, Nikita <inefedor@gmail.com> wrote:
> Hello, list. I want to propose generics. For those, who don't know what i=
t is, here's example: say we have a Comment class, that has a method getBod=
y. Also we have Collection class, that implements Traversable. Now, if I wa=
nt to validate all insertions into collection of comments, I would need to =
create CommentCollection class, extend it from Collection, and override all=
 the methods that are dealing with adding new elements to collection. Moreo=
ver, I can't have any hints from my IDE about type of collection's elements=
, so if I'll have code like this:
> foreach ($commentCollection as $comment) {
>     $comment->getBody();
> }
> There will be no way for IDE to know, of what type that object will be.
>
> But there's how I could solve my problem with generics:
> class Collection<T> implements Traversable
> {
>     ...
>     public function add(T $element){}
> }
> $collection =3D new Collection<Comment>();
>
> $collection->add(new Comment());
>
> $collection->add("that will be error");
>
> Actually, that's, again, all about type hinting. If we went so far with s=
calar type hinting, then generics would also be a good addition.
>
> So, what you think?


Hah, I had the use case often, and every OO programmer has met this
use case several time I think :
Here is an example with SplObjectStorage (which is a good starting
point structure for that) :

<?php
class MyClass extends SPlObjectStorage
{
    public function attach(MyType $o, $data =3D null) { /* throws an
E_STRICT we all know about */
        return parent::attach($o, $data);
    }
}

Solution :

<?php
class MyClass extends SPlObjectStorage
{
    public function attach($o, $data =3D null) {
        if (!$o instanceof MyType) {  /* That is both ugly and boring
to write */
            throw new \RuntimeException();
        }
        return parent::attach($o, $data);
    }
}

So, I'm +1 with the idea, but -1 with the proposed syntax.

I'm +1 with Lars, as this can be done with a "TypeAsString", this is
as well ugly, and I think we need PHP to provide a way to do that :

<?php
class Foo
{
    public function __construct($type) { $this->type =3D $type; }

    public function add($o)
    {
        if (!$o instanceof $this->type) {
            throw new \RunTimeException("type {$this->type} expected");
        }
        /* do something with $o*/
    }
}
class Bar { }
class Baz { }

$f =3D new Foo('bar');
$f->add(new Bar); /* OK */
$f->add(new Baz); /* KO */
$f->add(array()); /* KO */
?>

IMO : this is something the language should take care of, not the
developper, but that's my opinion :)