OOP in PHP: Class-function from a variable?

Question

Is it possible to call functions from class like this:

$class = new class;
$function_name = \"do_the_thing\";
$req = $class->$function_name();

Answer 1

My easiest example is:

$class = new class;
$function_name = "do_the_thing";
$req = $class->${$function_name}();

${$function_name} is the trick

Also works with static methods:

$req = $class::{$function_name}();