[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

<?php//如下面的类class MyClass
{    /**
     * 测试函数
     * 第一个参数必须为 OtherClass 类的一个对象
     */
    public function test(OtherClass $otherclass) {
        echo $otherclass->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 = &#39;Hello World&#39;;
}
?>

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