How to add a new method to a php object on the fly?

You can harness __call for this:

class Foo{    public function __call($method, $args)    {        if (isset($this->$method)) {            $func = $this->$method;            return call_user_func_array($func, $args);        }    }}$foo = new Foo();$foo->bar = function () { echo "Hello, this function is added at runtime"; };$foo->bar();

With PHP 7 you can use anonymous classes, which eliminates the stdClass limitation.

$myObject = new class {    public function myFunction(){}};$myObject->myFunction();

PHP RFC: Anonymous Classes

Using simply __call in order to allow adding new methods at runtime has the major drawback that those methods cannot use the $this instance reference.Everything work great, till the added methods don't use $this in the code.

class AnObj extends stdClass{    public function __call($closure, $args)    {        return call_user_func_array($this->{$closure}, $args);    } } $a=new AnObj(); $a->color = "red"; $a->sayhello = function(){ echo "hello!";}; $a->printmycolor = function(){ echo $this->color;}; $a->sayhello();//output: "hello!" $a->printmycolor();//ERROR: Undefined variable $this

In order to solve this problem you can rewrite the pattern in this way

class AnObj extends stdClass{    public function __call($closure, $args)    {        return call_user_func_array($this->{$closure}->bindTo($this),$args);    }    public function __toString()    {        return call_user_func($this->{"__toString"}->bindTo($this));    }}

In this way you can add new methods that can use the instance reference

$a=new AnObj();$a->color="red";$a->sayhello = function(){ echo "hello!";};$a->printmycolor = function(){ echo $this->color;};$a->sayhello();//output: "hello!"$a->printmycolor();//output: "red"