Proof of concept: generators versus array builders

fibonacci.php

#!/usr/bin/env php
<?php
/**
 * Fibonacci number creator.
 *
 * @param int $grandparent
 * @param int $parent
 * @return int
 */
function f(int $grandparent, int $parent): int
{
    return intval($parent + $grandparent);
}

/**
 * A classical fibonacci range builder.
 *
 * @param int $length
 * @return int[]
 */
function builder(int $length): array
{
    $grandparent = 0;
    $parent      = 1;
    $range       = [$grandparent, $parent];

    for ($i = 0; $i <= $length; $i++) {
        $child       = f($grandparent, $parent);
        $grandparent = $parent;
        $parent      = $child;
        $range[]     = $child;
    }

    return $range;
}

/**
 * Generator for fibonacci numbers.
 *
 * @param int $length
 *
 * @yields int
 */
function generator(int $length)
{
    $grandparent = 0;
    $parent      = 1;

    for ($i = 0; $i <= $length; $i++) {
        yield $child = f($grandparent, $parent);
        $grandparent = $parent;
        $parent      = $child;
    }
}

$maxNumIterations = 999999;

for ($numIterations = 0; $numIterations < $maxNumIterations; $numIterations++) {
    gc_collect_cycles();
    $builderUsage = 0;

    foreach (builder($numIterations) as $fibonacciNumber) {
        $currentUsage = memory_get_usage(false);

        if ($currentUsage > $builderUsage) {
            $builderUsage = $currentUsage;
        }
    }

    gc_collect_cycles();
    $generatorUsage = 0;

    foreach (generator($numIterations) as $fibonacciNumber) {
        $currentUsage = memory_get_usage(false);

        if ($currentUsage > $generatorUsage) {
            $generatorUsage = $currentUsage;
        }
    }

    echo sprintf(
        "#%d\tBuilder: %.2f kb\tGenerator: %.2f kb\t%d",
        $numIterations,
        $builderUsage / 1024,
        $generatorUsage / 1024,
        $fibonacciNumber
    ) . PHP_EOL;

    if ($builderUsage > $generatorUsage) {
        echo sprintf(
            'Found difference at iteration #%d and fibonacci number %d',
            $numIterations,
            $fibonacciNumber
        ) . PHP_EOL;
        break;
    }
}

See https://3v4l.org/C4IlF