PHP Recursive Function and Variable-Length Argument Lists

PHP Functions with Security Considerations - Part 3

Foreword: In this part of the series I talk about PHP Recursive Function and Variable-length Argument Lists.

By: Chrysanthus Date Published: 12 Nov 2018

Introduction

This is part 3 of my series, PHP Functions with Security Considerations. In this part of the series I talk about PHP Recursive Function and Variable-length Argument Lists. You should have read the previous parts of the series, before coming here, as this is the continuation.

Recursive Function
A recursive function is a function that keeps calling itself until a condition is met. Try the following code:

<?php

    function fnRecu($a)
        {
            if ($a < 20)
                {
                    echo "$a ";
                    $b = $a + 1;
                    fnRecu($b);
                }
        }

    fnRecu(0);

?>

The output is:

    0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

The function is called with an argument of 0. While the argument is less than 20, it is echoed for each execution of the function. For each execution, 1 is added to the argument and then the function is called again (with the sum). The calling stops when the argument to the function is 20.

Note: After at least 100 recalling in PHP, the script would stop running. Infinite recursion is considered a programming error in PHP. Comment at the bottom of this tutorial, and I will tell you how you can work-around (do not forget that you have to register, before you can comment).

Solution: do not code any recursive function that has more than 100 recursions. This is a limitation in PHP, which I think, can be worked-around still in PHP (comment below).

Variable-Length Argument Lists
Try the following code:

<?php

    function sum(...$numbers)
        {
            foreach ($numbers as $n)
                {
                    echo "$n ";
                }
        }

    sum(1, 2, 3, 4);

?>

The output is:

    1 2 3 4

The variable-length argument list scheme allows you to pass different number of arguments, in different calls, using one parameter. The different values will become consecutive members of the argument list. The scheme uses the token, ... in the parameter parentheses. It can also use the token in the calling argument, list as in the following code:

<?php

    function add($a, $b, $c)
        {
            $z = $a + $b + $c;

            echo $z;
        }

    $d = [10, 20, 30];
    add(...$d);

?>

The output is:

    60;

Here, the number of arguments is 1 (with ...), while there are 3 parameters

That is it for this part of the series. We stop here and continue in the next part.

Chrys

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PHP Recursive Function and Variable-Length Argument Lists

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