sprintf vs concat vs inline

<?php

declare(strict_types=1);

// SET UP

$iterations = 1000000;
$x = 'Custom Text';

$actions = array(
    "sprintf" => function () use ($x) {
        return sprintf('There some string: %s', $x);
    },
    "concat" => function () use ($x) {
        return 'There some string: '. $x;
    },
    "inline" => function () use ($x) {
        return 'There some string: $x';
    },
);

// --------------------------------

function benchmark($name, $iterations, $action)
{
    $startMemory = memory_get_usage(true);
    $startTime = microtime(true);

    for ($i = 0; $i <= $iterations; ++$i) {
        $a = $action();
    }

    $endTime = microtime(true);
    $endMemory = memory_get_usage(true);

    echo sprintf(
        'T: %.6f | M: %.2f | %s' . PHP_EOL,
        round($endTime - $startTime, 6),
        round($endMemory - $startMemory, 2),
        $name
    );
}

echo '<pre>' . PHP_EOL;

foreach ($actions as $name => $action) {
    benchmark($name, $iterations, $action);
}