Hashar noticed that for simple string literals, single quotes are faster than double quotes, if you count both parse time and execution time. This is reasonably easy to understand: single quotes have only two special characters, \ and ', so the loop body to process them would be simpler. Some people went on to assert that by extension $foo.' '.$bar is faster than "$foo $bar", without doing any benchmarks. I was never convinced of this. I did a benchmark where I had one file which looked like this: <?php $foo = 'foo'; $bar = 'bar'; echo " $foo $bar $foo $bar $foo $bar $foo $bar $foo $bar $foo $bar $foo $bar ... ?> And one file that looked like this: <?php $foo = 'foo'; $bar = 'bar'; echo $foo.' '.$bar.' '.$foo.' '.$bar.' '.$foo.' '.$bar.' '.$foo.' '.$bar. ... ?> There were 10000 "foo bar" strings output by each one. On my laptop, with no bytecode caching, string interpolation was 12 times faster than concatenation. Document Path: /test/concatenation.php Document Length: 80001 bytes Concurrency Level: 1 Time taken for tests: 7.420670 seconds Complete requests: 10 Failed requests: 0 Write errors: 0 Total transferred: 801670 bytes HTML transferred: 800010 bytes Requests per second: 1.35 [#/sec] (mean) Time per request: 742.067 [ms] (mean) Time per request: 742.067 [ms] (mean, across all concurrent requests) Transfer rate: 105.38 [Kbytes/sec] received Document Path: /test/string_interpolation.php Document Length: 82242 bytes Concurrency Level: 1 Time taken for tests: 0.610879 seconds Complete requests: 10 Failed requests: 0 Write errors: 0 Total transferred: 824080 bytes HTML transferred: 822420 bytes Requests per second: 16.37 [#/sec] (mean) Time per request: 61.088 [ms] (mean) Time per request: 61.088 [ms] (mean, across all concurrent requests) Transfer rate: 1316.14 [Kbytes/sec] received The slightly longer filesize in the string_interpolation.php case was because I used line breaks embedded in the string to break up powers of 10, whereas in concatenation.php the line breaks were not in the strings. The main reason I'm doing this is because I think $foo.' '.$bar looks ugly compared to "$foo $bar", and it also takes up more screen space. I doubt the performance gain would be significant either way, concatenation takes only 19us. I just don't like seeing the MediaWiki codebase uglied up for specious reasons. -- Tim Starling