Recursion

Recursion in PHP is a method or a function, which calls itself.

While the method calls itself, it also must have branch and not call itself : otherwise, the call will never end.

Functions, methods, closures and arrowfunctions may be recursive.

Recursion is an abstract notion : it is also used in the PHP name itself. PHP : Hypertext Preprocessor.

<?php

function factorial(int $number) {
    if ($number < 2) {
        return 1;
    }

    return ($number * factorial($number - 1));
}

// recursive closure
$factorial = function( $n ) use ( &$factorial ) {
    if( $n == 1 ) return 1;
    return $factorial( $n - 1 ) * $n;
};

?>

See also Recursion in PHP - when to use and how

Related : Functions