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Date: Sat, 11 Dec 2010 16:25:34 +0100
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To: Nathan Nobbe <quickshiftin@gmail.com>
Subject: Re: [PHP-DEV] Traits expecting interfaces implicitly leads to expensive runtime checks
From: php@stefan-marr.de (Stefan Marr)

Hi:

I added the proposal to the RFC.
See =
http://wiki.php.net/rfc/horizontalreuse#requiring_composing_class_to_imple=
ment_interface

=3D=3D=3D=3D=3D Requiring Composing Class to Implement Interface =3D=3D=3D=
=3D=3D

Traits are able to express required methods by using abstract method =
declarations.
An abstract method can be satisfied in varios ways, for instance by =
implementing it
in the composing class or by bringing it in from another Trait.

However, for traits that require complex interfaces to be satisfied, =
this approach is tedious
and fragile, since it requires the developer to state all used methods =
explicitly.

Another solution is that a Trait expresses a requirement for the =
composing class to implement
a certain interface. This is not entirely identical to using abstract =
methods, however.
First, it imposes a requirement on interface level and thus will have =
the same fragility
with respect to interface changes as all other clients of an interface.
On the other hand, it avoids duplications of abstract method definitions =
and makes
the interface the main entity of responsibility as for normal =
client-interface uses
in current code.

<?php
// IteratorUser works with $this using the Iterator interface
trait IteratorUser require Iterator {
    function foo() {
        $next =3D $this->next();
        ...
    }
}

// composed into a class that needs to implement the interface
class Example implements Iterator {
  use IteratorUser;
}

Are there any objections to implementing this?

Thanks
Stefan


--=20
Stefan Marr
Software Languages Lab
Vrije Universiteit Brussel
Pleinlaan 2 / B-1050 Brussels / Belgium
http://soft.vub.ac.be/~smarr
Phone: +32 2 629 2974
Fax:   +32 2 629 3525