Sometimes we need to populate static variables in php (e.g. populating associative arrays from existing arrays). Easiest way is to define a static function (e.g. init()) and then call it statically after the class.
<?php class Foo { static $a = ["foo", "bar"]; static $aa = array(); static function init () { foreach (self::$a as $val) { self::$aa[$val] = 1; } } } Foo::init(); print_r(Foo::$aa); ?>
Array ( [foo] => 1 [bar] => 1 )
Env: PHP 7.4.33 (Linux)