It does have the MustCompile outside of the loop. I pasted the wrong link originally.
Ah, my apology I saw the earlier link.
If I am reading the chart correctly, doubled performance would still not be enough.
Absolutely. But the original version linked was twice as slow as need be.
For trivial replacements string manipulation I find is faster and safer (fewer bugs). But there is some threshold of complexity in which regular expressions are both more performant and safer.
MustCompile is generally used to make the regexp a global so that it isn't done over and over.
Just move it out of the loop, as it's really not necessary to compile regular expressions every time you want to match/replace against it.