PHP - Callable method not as array

Question

Usually in PHP if you have a method bar of a class Foo and you'd like to pass it around as a callable, you use something like

$foo = new Foo();
$callable = [$foo, 'bar'];

The downside of this is that is_array($callable) evaluates to true.

Is there another feasible way to pass around a class method as a callable such that is_array($callable) returns false?

Answer 1

PHP 7.1 finally took a big steep in making callbacks first-class citizens via Closure::fromCallable (RFC).

As described here, you can use it like this:

class MyClass
{
  public function getCallback() {
    return Closure::fromCallable([$this, 'callback']);
  }

  public function callback($value) {
    echo $value . PHP_EOL;
  }
}

$callback = (new MyClass)->getCallback();
$callback('Hello World');

Using it has some benefits:

• Better error handling - When using Closure::fromCallable, it shows errors in the right place instead of showing it where we are using the callable. This makes debugging a lot easier.

• Wrapping scopes - The above example will work fine even if the callback is a private/protected method of MyClass.

• Performance - This can also improve the performance by avoiding the overhead of checking if the given callable is actually a callable.

Answer 2

Functions and methods are not first class citizens in PHP, i.e. they cannot be assigned to variable, do not have a type etc.

callable isn't actually a type, is_callable as well as the callable type hint just checks if something can be used as a function. This can be:

• an array [class, method] for a static method
• an array [object, method] for an instance method
• a string for a function
• a Closure instance
• an object that implements the magic method __invoke()

As you see, all of these values actually have a different type and just happen to be "callable". There is no such thing as a "pure" callable that does not have another type.