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To: php-dev <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=001e680f116023b7da046a01525b
Subject: Suggestion on static field inheritance
From: diogin@gmail.com (Jingcheng Zhang)

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Content-Type: text/plain; charset=ISO-8859-1
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Hello all,

Maybe I have not found its detailed description on PHP's official manual,
but PHP does allow static field inheritance. However there is a little
difference between dynamic field inheritance and static field inheritance,
as the following codes shows:

<?php
class static_a {
    public static function change($name) {
        self::$name = $name;
    }
    public static $name = 'a';
}
class static_c extends static_a {}
class static_d extends static_a {}

echo static_a::$name; // a
static_c::change('c');
echo static_a::$name; // c
static_d::change('d');
echo static_a::$name; // d


class dynamic_a {
    public function change($name) {
        $this->name = $name;
    }
    public $name = 'a';
}
class dynamic_c extends dynamic_a {}
class dynamic_d extends dynamic_a {}

$a = new dynamic_a();
$c = new dynamic_c();
$d = new dynamic_d();
echo $a->name; // a
$c->change('c');
echo $a->name; // a
$d->change('d');
echo $a->name; // a
?>

The result of static inheritance test can be meaningful on some
way(especially on class-based programming perspective), but when considering
the static class as "object" in prototype-based programming(which I doubt is
some people's favourite who comes from prototype-based OOP community), this
result can be confusing. On JavaScript, this example can be:

<script type="text/javascript">
function extends(parent) {
    var T = function () {};
    T.prototype = parent;
    return new T();
}
var static_a = {
    name: 'a',
    change: function (name) {
        this.name = name;
    }
};
var static_c = extends(static_a);
var static_d = extends(static_a);

alert(static_a.name); // a
static_c.change('c');
alert(static_a.name); // a
static_d.change('d');
alert(static_a.name); // a
</script>

This looks more meaningful. So my suggestion is, could PHP's static
inheritance rule follow the dynamic inheritance rule ( $this on dynamic, or
prototype delegation on JavaScript) ?
Thanks :-)

-- 
Best regards,
Jingcheng Zhang
P.R.China

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