PHP's Magic __invoke() Method and the Callable Typehint

PHP has a variety of magic methods; methods named with two underscores at the start, which get called automatically when a particular event happens. In PHP 5.3, a new magic method was added: __invoke().


The __invoke() method gets called when the object is called as a function. When you declare it, you say which arguments it should expect. Here's a trivially simple example:

class Butterfly {
  public function __invoke() {
    echo "flutter";

We can instantiate a Butterfly object, and then just use it like a function:

$bob = new Butterfly();
$bob(); // flutter

If you try to do the same thing on an object without an __invoke() method, you'll see this error:

PHP Fatal error:  Function name must be a string in filename.php on line X

We can check if the object knows how to be called by using the is_callable() function.

Callable Typehint

In PHP 5.4 (the newest version, and it has lots of shiny features), we have the Callable typehint. This allows us to check whether a thing is callable, either because it's a closure, an invokable object, or some other valid callback. Another trivial example to continue the butterflies and kittens theme:

function sparkles(Callable $func) {
  return "fairy dust";

class Butterfly {
  public function __invoke() {
    echo "flutter";

$bob = new Butterfly();
echo sparkles($bob); // flutterfairy dust

So there it is, one invokable object being passed into a function and successfully passing a Callable typehint. I realise I also promised kittens, so here's a cute silver tabby I met the other day:


11 thoughts on “PHP's Magic __invoke() Method and the Callable Typehint

  1. Btw, pretty much nobody uses __invoke in PHP, but it is something very common in other languages. E.g. in C++ you commonly define Functor classes:

    class Hasher {
    unsigned long operator()(const Obj& obj1, const Obj& obj2) {
    return ...;

  2. Thank you Lorna, I needed to know exactly why and how the __invoke() method in ZF 2 helpers works. This post was the third in search results and the first with a good title.

    @Nikita Everybody using ZF 2 with view helpers uses __invoke a lot.

  3. just want to say that what is true one day is a not next day, or it was never true :)
    a lot of invoke usage in architectures EBI with interactors on silex, symfony2 and libraries.

  4. The Callable type hint is awesome but what if I want to check in an if/else situation?
    instanceof Callable does not appear to work.

    $bob = "blah";

    if($bob instanceof Callable) {
    echo "x";

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  7. In my case, __invoke has come in handy when I wanted to transform the class autoloading process into an OOP one:
    - I created a class that acts as an autoloader for a specific location where classes are stored.
    - I can then pass this class to spl_autoload_register which takes a callable as first argument and will indeed be able to load a class upon request using the Autoload object provided.
    Just to give you an idea of what I mean:
    define('AUTOLOAD_EXTENSION_SUFFIX', '.php');

    class Autoload {
    public static Autoload function register(string $base_path = null, string $path_suffix = null, bool $throw = true, bool $prepend = false);
    public static bool function testPath(string $path);
    public string function unify(string $class_name, string $base_path = null, string $path_suffix = null);
    public mixed function __invoke(string $class_name);
    To get back on __invoke, in this case Autoload::register will create a new Autoload object and pass it to spl_autoload_register and return Autoload object.


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