Mutators for C# 9 Pattern Matching

[hannahchan]

I'm only just learning about this now so this might not make sense. I've got code like this;

if (myInput is not null)
{
    doSomething();
}

The is not pattern combination is new to C# 9 and Stryker is currently unable to mutate it. It looks like there are other pattern operators such as and and/or or 😄 . It would be nice to have mutators for those as well.

Someone will need to take a look at the pattern matching specification of C# 9. The following might help.

https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-9.0/patterns3

[rouke-broersma]

Pattern matching mutators would be awesome :)

[richardwerkman]

I think there is not much else than not, and and or. So the mutator would look like:

Pattern matching

Original	Mutated
is	is not
is not	is
and	or
or	and

We could also remove brackets like:

bool IsLetter(char c) => c is (>= 'a' and <= 'z') or (>= 'A' and <= 'Z');

bool IsLetter(char c) => c is >= 'a' and <= 'z' or >= 'A' and <= 'Z';

[rouke-broersma]

Those are the interesting new operators to mutate, but I don't think we're currently mutating all existing pattern matching values since sometimes they need to be static. There might also be some fun stuff we could do with the is Type pattern matching. For example change an is Type pattern to a is var pattern.

[rouke-broersma]

Implemented by #2313 for switch patterns