Counter Functions In Loops

ID

php.counter_functions_in_loops

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Efficiency

Language

Php

Tags

efficiency, performance

Description

Reports a call to a size-counting function such as count() or sizeof() inside the condition of a for or while loop. The condition is evaluated before every iteration, so the count is recomputed on each pass instead of once.

Rationale

A loop condition runs on every iteration. Calling count($items) there asks PHP to size the same array again and again, adding a per-iteration cost that grows with the number of passes. For a loop that already walks the collection, this effectively doubles the work. Computing the size once, before the loop, and comparing against the cached value removes the repeated calls without changing behaviour.

<?php
function sum(array $items): int
{
    $total = 0;
    for ($i = 0; $i < count($items); $i++) {  // FLAW - count() runs on every iteration
        $total += $items[$i];
    }

    $n = count($items);                        // OK - size computed once
    for ($i = 0; $i < $n; $i++) {
        $total += $items[$i];
    }
    return $total;
}

Remediation

Compute the size once into a local variable before the loop and compare against that variable in the condition. When the collection can change inside the loop, recompute the cached size explicitly at the point it changes rather than on every iteration.

References