Introduce Type Hinting In PHP5

Introduction

This article explains type hinting using PHP5. PHP5 introduces type hinting. Functions square measure are currently able to force parameters to be objects by specifying the name of the category within the operate prototype, interfaces, arrays or callback hint type. However, if null values are employed because the default parameter value then it'll be allowed as an associate argument for any later decision. If the category or interface is nominative as a type hint then all its kids or implementations square measure are allowed too. Type hints can't be used with scalar sorts like int or string. Resources and Traits don't seem to be allowed either. In type hinting, a function is able to force a parameter to be an object by the specific name of the class. If you pass the null parameter then it will be allowed as arguments. I will show that in the last example of allowing null values as arguments.

A Valid type class of unit category names for arguments that receive objects and array for those who receive arrays. I will show use of this example.

Type hint example class

In this example I will show a simple type hint.

<?php
class hint
{
    public function demo(newclass $overclass) {
        echo $overclass->var;
    }
    // use first parameter like an array
    public function demo_array(array $input_array) {
    echo "<pre>"; print_r($input_array);
    }
    //use first parameter must be an iterator
    public function demo_interface(Traversable $iterator) {
        echo get_class($iterator);
    }
    //use first parameter must be a collable
    public function demo_callable(callable $callback, $demo) {
        call_user_func($callback, $demo);
    }
}
class newclass {
    public $var = 'this is my hint type';
}
?>

Failure to satisfy the type hint results in a catchable error.

 <?php
include 'demo.php';
$hint = new hint;
$overclass = new newclass;
//show fatal error must be an object class
$hint->demo('hello');
// Fatal Error: arguments one must be an instance of newclass
$foo = new testClass;
$hint->demo($foo);
// Fatal Error: Argument first must not be null
$hint->demo(null);
//here show my hint class
$hint->demo($overclass);
// here show fatel error use arguments one must be an array
$hint->demo_array('a string');
// show array
$hint->demo_array(array('a', 'b', 'c'));
//show the array object
$hint->demo_interface(new ArrayObject(array()));
// show the integer value one
$hint->demo_callable('demo_dump', 1);
?>

Output

Type hinting also works with functions as in the following

 <?php
class hint {
    public $demo = 'this is my hint class also work with function';
}
function hintFunction(hint $foo) {
    echo $foo->demo;
}
$hint = new hint;
hintFunction($hint);
?>

Output

 

Type hinting allowed null value

This example will show a fatal error.

 <?php
function demo(testClass $obj = NULL) {
}
demo(NULL);
demo(new testClass);
?>

Output