任何方式添加新方法到PHP中的对象，如javascript？

any way to add new method to an object in php such as javascript?

in javascript we can extend an js obj like this

var o={};
o.test1 = function(){...}

how to do it in php? please see my code bellow:

<?php

class a{
    function test(){
        echo 'hello';
    }
}

$var= new a;

// I want to add a new method fo $var
// .... how to extend $var here ?

$var->test1();  // world

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you can extend your object : (note : this is not my code, I just copy this code is from documentation php extends class)

<?php

class foo
{
    public function printItem($string)
    {
        echo 'Foo: ' . $string . PHP_EOL;
    }

    public function printPHP()
    {
        echo 'PHP est super' . PHP_EOL;
    }
}

class bar extends foo
{
    public function printItem($string)
    {
        echo 'Bar: ' . $string . PHP_EOL;
    }
}

$foo = new foo();
$bar = new bar();
$foo->printItem('baz'); // Affiche : 'Foo: baz'
$foo->printPHP();       // Affiche : 'PHP est super'
$bar->printItem('baz'); // Affiche : 'Bar: baz'
$bar->printPHP();       // Affiche : 'PHP est super'

?>