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How to Define Class Properties with Complex Default Values in PHP
How to Define Class Properties with Complex Default Values in PHP
Oct 20, 2024 pm 01:47 PM
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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