Question

Is it possible to create a PHP class that would act like this:

class Foo
{
    function __construct($param)
    {
        if (!is_numeric($param))
        {
            // stop class
        }
    }
}

$a = new Foo(2);
$b = new Foo('test');

var_dump($a);
var_dump($b);

which will return

object(Foo)[1]
null

Answer 1

The only way I’m aware of to stop creating of a new object while not immediately terminating the script is to throw an exception:

class Foo {
    public function __construct($param) {
        if (!is_numeric($param)) {
            throw new \InvalidArgumentException('Param is not numeric');
        }
    ...
}

Of course, you’d have to be sure and catch the exception in the calling code and handle the problem appropriately.