What's the fastest way of concatenating strings in PHP?

Question

I want to combine two variables together:

$var1 = 'Welcome ';

$var2 = $_SESSION['UserName'];

Which of these will work faster? Code sample 1:

$var3 = $var1.$var2;

Or code sample 2:

$var3 = "$var1$var2";

Answer 1

Code sample 1 won't work at all..

Syntax considerations set aside, Sample 1 should be trivially faster because it doesn't involve parsing a string (looking for variables).

But it's very, very trivial..