php - check if class name stored in a string is implementing an interface

Question

I understand that my question is somehow wrong, but I'm still trying to solve this problem.

I have an interface Programmer:

interface Programmer {     public function writeCode(); } 

and a couple of namespaced classes:

• Students\BjarneProgrammer (implements Programmer)
• Students\CharlieActor (implements Actor)

I have this class names stored in array $students = array("BjarneProgrammer", "CharlieActor");

I want to write a function, that will return an instance of class if it's implementing Programmer interface.

Examples:

getStudentObject($students[0]); - It should return an instance of BjarneProgrammer because it's implementing Programmer.

getStudentObject($students[1]); - It should return false because Charlie is not a Programmer.

I tried it using instanceof operator, but the main problem is that I do not want to instantiate an object if it's not implementing Programmer.

I checked How to load php code dynamically and check if classes implement interface, but there is no appropriate answer as I don't want to create object unless it's returned by function.

Answer 1

You can use class_implements (requires PHP 5.1.0)

interface MyInterface { } class MyClass implements MyInterface { }  $interfaces = class_implements('MyClass'); if($interfaces && in_array('MyInterface', $interfaces)) {     // Class MyClass implements interface MyInterface } 

You can pass the class name as a string as function's argument. Also, you may use Reflection

$class = new ReflectionClass('MyClass'); if ( $class->implementsInterface('MyInterface') ) {     // Class MyClass implements interface MyInterface } 

Update : (You may try something like this)

interface Programmer {     public function writeCode(); }  interface Actor {     // ... }  class BjarneProgrammer implements Programmer {     public function writeCode()     {         echo 'Implemented writeCode method from Programmer Interface!';     } } 

Function that checks and returns instanse/false

function getStudentObject($cls) {     $class = new ReflectionClass($cls);     if ( $class->implementsInterface('Programmer') ) {         return new $cls;     }     return false; } 

Get an instance or false

$students = array("BjarneProgrammer", "CharlieActor"); $c = getStudentObject($students[0]); if($c) {     $c->writeCode(); } 

Answer 2

If you're using a modern version of PHP (5.3.9+), then the easiest (and best) way would be to use is_a() with the third parameter true:

$a = "Stdclass";  var_dump(is_a($a, "stdclass", true)); var_dump(is_a($a, $a, true)); 

Both of those will return true.