How to Define Class Properties with Complex Default Values in PHP

Workaround for Basic Syntax Not Being Parsed

PHP's strict syntax rules can be a hurdle when defining class properties with complex default values. While syntax like (1 << 0) might seem straightforward, PHP considers it an expression with side effects, not a valid default value in class declarations.

Understanding PHP's Class Declaration Limitations

In PHP, default values for class constants or properties must be primitive values, such as:

const ABC = 8;
static $GHI = 15;

This restriction stems from the principle that declarative statements should not create side effects.

Creating User-Defined Types and Initializing with Expressions

To overcome this limitation, we can create user-defined types and initialize them with expressions outside the class declaration:

class SDK {

    // Example of self-created type
    static private $STRING_NONE = 1 << 0;

}

$fString = SDK::$STRING_NONE;

Refactoring the Original Class

Applying this workaround to the original class example:

class SDK {

    static private $_types = null;

    static public function getType($type_name) {
        self::_init_types();
        return self::$_types[$type_name];
    }

    static private function _init_types() {
        if (!is_array(self::$_types)) {
            self::$_types = array(
                'STRING_NONE' => 1 << 0,
                // ... rest of types here
            );
        }
    }

    function __construct($fString = null) {
        if (is_null($fString)) {
            $fString = self::getType('STRING_NONE') & self::getType('STRING_HOSTS');
        }
    }

}

$SDK =& new SDK(SDK::getType('STRING_HOSTS'));

This approach allows us to define and use types within the class while accommodating default values that are the result of expressions.
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