Pass StringValues via in

[benaadams]

Depends on dotnet/extensions#311 (for perf)

Resolves #2301

[halter73]

This is already compiling despite dotnet/extensions#311 not being merged. Does the struct not need to be marked as readonly to use the in keyword for parameters? Do we still need to merge both PRs to avoid the copy?

[benaadams]

Does the struct not need to be marked as readonly to use the in keyword for parameters?

Nope :-|

You can read fields of a non-readonly struct without it causing a copy; but not properties or methods (will cause copy)

Also changing to in is a code compatible change (not binary compatible).

Do we still need to merge both PRs to avoid the copy?

Yep

[benaadams]

As aside it will give an error when in is used with a generic constraint dotnet/roslyn#24601 (comment) because its what can be specified on an interface; which is only properties and methods and no fields; thus is generally bad.

Is talk in that issue of adding a readonly struct constraint to allow it when it wouldn't be counter productive.

[halter73]

I'm OK to merge this as soon as dotnet/extensions#311 is merged. I'll want to see benchmark numbers ofc.

[davidfowl]

I'll merge it once the CI runs against the latest Common