Speed up Regex performance with .NET 5

Thanks for the nice write-up, Marcus. One issue I noticed in your final benchmark on Regex. Regex.Matches is lazy, meaning it doesn't actually execute the regex until it needs to. When you run Regex.Matches, it's just fetching the relevant regex from the cache (or parsing/compiling it if it can't find it), and returning to you the collection object that will enable you to retrieve all the matches, but it hasn't done any matching yet. It's only when you iterate the collection, ask for its Count, index into it, etc., that it will compute as little as it needs to in order to answer your question (e.g. if you ask for matches[2], it'll ensure it has the 0th, 1st, and 2nd matches, but it needn't go beyond that yet). So in your benchmark, it's not actually running the regex at all. That's also why, even though the three regexes being tested have various levels of complexity, the benchmarks are all coming back as approximately the same answer. I'd suggest redoing the benchmark with .Count appended to each Matches call, or something like that.