<?
$str1 = $str2 = "";

for ($i=0; $i < 10000; $i++) {
	$start = microtime(true);
	$str1 .= 'You got ' . $i . ' messages';
	$str1_test[] = microtime(true) - $start;
}

echo "Dotted: " . ($str1_result = array_sum($str1_test) / 10000);

echo PHP_EOL;

for ($i=0; $i < 10000; $i++) {
	$start = microtime(true);
	$str2 .= "You got {$i} messages";
	$str2_test[] = microtime(true) - $start;
}

echo "Interpolated: " . ($str2_result = array_sum($str2_test) / 10000);
echo PHP_EOL . ($str2_result < $str1_result ? "Interpolation" : "Dot") . " is faster!";