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webmaster at removethis dot weird-webdesign dot de ¶
15 years ago
On PHP 5.2.x or previous you might run into problems initializing static variables in subclasses due to the lack of late static binding:

<?php
class A {
    protected static $a;
    
    public static function init($value) { self::$a = $value; }
    public static function getA() { return self::$a; }
}

class B extends A {
    protected static $a; // redefine $a for own use
    
    // inherit the init() method
    public static function getA() { return self::$a; }
}

B::init('lala');
echo 'A::$a = '.A::getA().'; B::$a = '.B::getA();
?>

This will output:
A::$a = lala; B::$a = 

If the init() method looks the same for (almost) all subclasses there should be no need to implement init() in every subclass and by that producing redundant code.

Solution 1:
Turn everything into non-static. BUT: This would produce redundant data on every object of the class.

Solution 2:
Turn static $a on class A into an array, use classnames of subclasses as indeces. By doing so you also don't have to redefine $a for the subclasses and the superclass' $a can be private.

Short example on a DataRecord class without error checking:

<?php
abstract class DataRecord {
    private static $db; // MySQLi-Connection, same for all subclasses
    private static $table = array(); // Array of tables for subclasses
    
    public static function init($classname, $table, $db = false) {
        if (!($db === false)) self::$db = $db;
        self::$table[$classname] = $table;
    }
    
    public static function getDB() { return self::$db; }
    public static function getTable($classname) { return self::$table[$classname]; }
}

class UserDataRecord extends DataRecord {
    public static function fetchFromDB() {
        $result = parent::getDB()->query('select * from '.parent::getTable('UserDataRecord').';');
        
        // and so on ...
        return $result; // An array of UserDataRecord objects
    }
}

$db = new MySQLi(...);
UserDataRecord::init('UserDataRecord', 'users', $db);
$users = UserDataRecord::fetchFromDB();
?>

I hope this helps some people who need to operate on PHP 5.2.x servers for some reason. Late static binding, of course, makes this workaround obsolete.
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