How to use type constraints to qualify PHP function types

PHP 5 can use type constraints. The parameters of a function can specify data that must be an object type or an array type or a recursive type or a callback type;

<?php//class myclass{    /**     * Test function     * The first parameter must be an object of the Otherclass class * * Public    function test ( Otherclass $otherclass) {        echo $otherclass->var;    }    /**     * Another test function     * The first parameter must be an array */public    function test_array (array $input _array) {        Print_r ($input _array);}    }    /**     * The first parameter must be a recursive type     *    /Public Function test_interface (traversable $iterator) {        echo get_class ($ iterator);    }        /**     * The first parameter must be a callback type */public    function test_callable (callable $callback, $data) {        Call_user_func ( $callback, $data);}    } Otherclass class Otherclass {public    $var = ' Hello world ';}? >

A catch fatal error is thrown when the parameters of a function call are inconsistent with the defined parameter type.

<?php//object of two classes $myclass = new MyClass; $otherclass = new otherclass;//fatal error: The first argument must be an object of the Otherclass class $myclass->test (' hello ');//Fatal error: The first parameter must be an instance of the Otherclass class $foo = new StdClass; $myclass->test ($foo);//Fatal error: The first parameter cannot be null$myclass- >test (null);//correct: Output Hello world $myclass->test ($otherclass);//Fatal error: The first parameter must be an array $myclass->test_array (' A String ');//correct: Output array $myclass->test_array (Array (' A ', ' B ', ' C '));//correct: Output Arrayobject$myclass->test_interface ( New Arrayobject (Array ()));//correct: Output int (1) $myclass->test_callable (' Var_dump ', 1);? >

Type constraints are not only used in the member functions of a class, but also in functions.

<?php//class MyClass {public    $var = ' Hello world ';} /** * Test function * The first parameter must be an object of the MyClass class */function MyFunction (MyClass $foo) {    echo $foo->var;} Correct $myclass = new MyClass; MyFunction ($myclass);? >

Type constraints allow NULL values

<?php/* accepts NULL values */function Test (StdClass $obj = null) {}test (null); Test (new StdClass);?