Kestrel should create strings using newer idiomatic method

[benaadams]

Currently uses string key = new string('\0', keyLength) and then mutates with fixed.

Should use something more like string.Create

However, attention needs to be given to avoid any performance regressions.

/cc @GrabYourPitchforks @davidfowl

[gfoidl]

to avoid any performance regressions

Especially on small string-lengths, as the cost for the delegate invocation may be quite high in relation to actual work. new string(Span) may be faster in these cases.

[GrabYourPitchforks]

Thanks for opening this! 😃

[gfoidl]

FYI: I gave this a try. Perf results don't look so bad so far, but I need more testing for the other methods, then I'll submit a PR.

[GrabYourPitchforks]

I imagine that once static function pointers come online there would be string.Create overloads that would allow using those, which should also help eke out just a little bit greater perf.

[gfoidl]

Yeah, I hope so too. That can open a door for a lot of "delegate" usages, and make some generic-struct-tricks obsolete.

[gfoidl]

@halter73 this issue can be closed, as the PR got merged?