On Aug 16, 2007, at 5:48 PM, Alvaro Carrasco wrote:
Richard K Miller wrote:
Here's an OOP question that perplexes me. It seems PHP doesn't
treat static variables correctly in child classes.
<?php
class ABC {
public $regular_variable = "Regular variable in ABC\n";
public static $static_variable = "Static variable in ABC\n";
public function regular_function() {
echo $this->regular_variable;
}
public static function static_function() {
echo self::$static_variable;
}
}
class DEF extends ABC {
public $regular_variable = "Regular variable in DEF\n";
public static $static_variable = "Static variable in DEF\n";
}
$abc = new ABC();
$abc->regular_function();
ABC::static_function();
$def = new DEF();
$def->regular_function();
DEF::static_function();
?>
WHAT I EXPECTED:
Regular variable in ABC
Static variable in ABC
Regular variable in DEF
Static variable in DEF
ACTUAL OUTPUT:
Regular variable in ABC
Static variable in ABC
Regular variable in DEF
Static variable in ABC <--- This is different from what I expected
Anyone know why?
Richard
"self" is bound to the class at compile time, not at runtime. So
when you do:
echo self::$static_variable
It's the same as doing
echo ABC::$static_variable
because "self" was bound to ABC when the class was defined.
It is more of an implementation limitation in php than an intended
feature.
For version 6, the php dev team is considering to do late-static
binding, which would bind "self" to a class at runtime instead of
compile time, but they haven't flushed out all of the details.
Alvaro
Alvaro, thanks for this explanation; this was very helpful. I
sincerely hope that PHP6 implements late static binding.
Do you see anyway around this? My parent class is a generic database
table wrapper to provide ORM mapping. Each child class maps to a
specific table. I'd like to implement several static functions such
as search_by(), a factory pattern that returns an object or objects
of its own class that match the search. I see no way to define the
database table in a child class and have it passed back to a static
function in the parent class.
Richard
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