When coding php pages you often have to manipulate strings and print them, with select pieces of data, so that the user can see them.

There are 2 different ways to do this:

$var = 'This is a variable : '.$data;

and

$var = "This is a variable : $data";

In the first case, you just concat the 2 elements together, whereas in the second case, php does the substitutions by it’s self.

The interesting part is that the first construct is over 4 times faster than the second….

More info (in French) here