[php classes and objects] type constraints

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Type constraints

PHP 5 can use type constraints.

The parameters of the function can be specified as:

• Object (specify the name of the class in the function prototype)

• Interface

• Array (PHP 5.1)

• callable (PHP 5.4)

If using NULL as The default value of the parameter, then NULL can still be used as the actual parameter when calling the function.

If a class or interface specifies a type constraint, so do all its subclasses or implementations.

Type constraints cannot be used for scalar types such as int or string. Traits are not allowed either.

Example #1 类型约束示例 var; } /** * 另一个测试函数 * 第一个参数必须为数组 */ public function test_array(array $input_array) { print_r($input_array); } } /** * 第一个参数必须为递归类型 */ public function test_interface(Traversable $iterator) { echo get_class($iterator); } /** * 第一个参数必须为回调类型 */ public function test_callable(callable $callback, $data) { call_user_func($callback, $data); } }// OtherClass 类定义class OtherClass { public $var = 'Hello World'; } ?>

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