Depth

Depth is a measure of how many an operation has been repeatedly applies, over and over.

It applies to several concepts:

• Multi-dimensional array depth: $array['d1']['d2']['d3']['d4']

• Recursion depth: see example

• Nested loop depth: number of loops inside a loop

• Callstack depth: number of functions calling another one

• Object inheritance depth: the maximum number of extension levels in a class hierarchy

Depth might be limited, when it is prevented from going beyond a certain level, or unlimited, when there is no such limit. For example, xdebug offers a directive called xdebug.max_nesting_level that limits nesting depth.

<?php

    // The recursion depth is limited to 5
    function foo($level = 0) {
        if ($level < 5) {
            return foo($level + 1);
        }
        return 1;
    }

?>

Related : Callstack