According to the documentation in VB6 the Mid function returns a variant, but Mid$ returns a string and apparently this is more efficient.
My questions are :
What simple test can I use to discern the difference in performance ? I tried looking at simple app which did a few string operations, with Perfmon, but there was no discernible difference.
Is it worth worrying about? I've gotten into the habit of using the $-ized functions, but should I recommend everybody on my team to use it as well ?
Isn't worth worrying about. It's a remnant from Microsoft Basic of 15-20 years ago when a fast processor was orders of magnitude slower than anything today.
It has a certain esthetic appeal to use Mid$ rather than let VB determine what your datatypes are, though. And if you have any loops that are executing it, say, thousands of tiems a second, then your curiosity factor might increase. Otherwise, neh.
Here's a link to someone who measured the difference. Mid$ was about 2.5 times as fast as Mid. Including tests going back to VB4.
Honestly, I think it's negligible.
Maybe you can try something like this. Download the "High-Performance Timer Object" from http://ccrp.mvps.org/, do a long loop (1.000.000 iterations or so) of string operations, and measure the run time difference. By "operations" I mean: Concatenation of Variants as opposed to concatenation of Strings. Mid() and Mid$() will very likely perform the same. OTOH - you can test that as well.
If you did, I'd be interested if you posted the results.
Whilst performance between them is negligible its not really a differentiator as to which to use anyway.
There can be some nuances when using a variant when a strong type is required. For example what happens when you pass a variant to a parameter expecting a ByRef string? Nothing bad but something a little more than passing an address happens.
Hence if you know that you want to work with strings then go ahead and use the $ versions of these functions the behaviour of them and their use in other expressions is simpler and better understood. If you know you need a variant and your inputs are variants then sure use the non $ versions.