Closures and Callables

Anonymous function

Anonymous functions, as the name suggests, are functions without a name. Anonymous functions are functions defined on the spot, and they can be stored in a variable.

Anonymous functions are also called Lambdas.

A Lambda can be assigned to a variable or passed to another function as an argument. If you are familiar with other programming languages like Javascript or Ruby, you will be very familiar with anonymous functions.

$mySumFunction = function($a,$b){
    return $a+$b;

// Will output: 13
echo $mySumFunction(5,8);


In PHP a closure is actually a Class used to represent anonymous functions. Besides the methods listed here, this class also has an __invoke() method. This is for consistency with other classes that implement calling magic, as this method is not used for calling the function.

The __invoke() method allows objects to be called as functions.


class MsgClass
    public function __invoke($name, $salutation='Hello')
        return $salutation . ', ' . $name . '!';

$msg = new MsgClass();

 // will output "Hello, World!"
echo $msg('World');

Closure Example


// Create a user
$user = "Philip";

// Create a Closure
$greeting = function() use ($user) {
  echo "Hello, $user";

// Returns "Hello, Philip"

If you want to read more about Lambdas and Closures, you can look at the article below What are Lambdas and Closures?


Callbacks can be denoted by callable type hint as of PHP 5.4. PHP documentation used callback type information for the same purpose

Some functions like call_user_func() or usort() accept user-defined callback functions as a parameter. Callback functions can not only be simple functions, but also object methods, including static class methods.

A callable can be:

  • a string containing an existing function name (eg.: strpos())
  • a string containing a class method name (eg.: MyClass::MyObject()
  • an anoymous function (eg.: $mySumFunction, or the actual declaration)
  • a closure
  • an invokable object

Sources: What are PHP Lambdas and Closures? PHP: Closure - Manual PHP: Callbacks / Callables

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