Benchmarks merging two arrays using array_merge and classic foreach loop with manual addition.

benchmark_array_merge_vs_foreach_manual_addition.php

<?php

class Benchmark
{
    /**
     * @param string $mergeStrategy
     * @param int    $arrayToMergeSize
     *
     * @return void
     */
    public function run(string $mergeStrategy, int $arrayToMergeSize): void
    {
        $startMicrotime = microtime(true);

        $mergedArray = [];
        $extraBigArrayToMerge = [];

        for ($i = 0; $i < 1000000; $i++) {
            $mergedArray[] = 'hardcoded:'.$i;
        }

        for ($i = 0; $i < $arrayToMergeSize; $i++) {
            $extraBigArrayToMerge[] = 'extra:'.$i;
        }

        if ($mergeStrategy === 'array_merge') {
            $mergedArray = array_merge($mergedArray, $extraBigArrayToMerge);
        }

        if ($mergeStrategy === 'normal') {
            foreach ($extraBigArrayToMerge as $element) {
                $mergedArray[] = $element;
            }
        }

        $endMicrotime = microtime(true);

        echo sprintf(
            "Merging two arrays using '%s' strategy took %d seconds.\n",
            $mergeStrategy,
            $endMicrotime - $startMicrotime
        );

        echo sprintf(
            "Memory usage is: %d MB.\n",
            memory_get_usage() / 1024 / 1024
        );

        echo sprintf(
            "Memory peak was: %d MB.\n",
            memory_get_peak_usage(true) / 1024 / 1024
        );
    }
}

$mergeStrategy = $argv[1];
$extraBigArraySize = $argv[2];

$benchmark = new Benchmark();
$benchmark->run($mergeStrategy, $extraBigArraySize);