Extracting separate ArgumentMatcher ifc with no FailureMessage

[yhrn]

Since FailureMessage() is only used for invocation count matching this will significantly simplify writing custom argument matchers - one less method to implement, no need for mutable state and synchronization.

[petergtz]

I think that's a great idea! I think when I introduced the matcher concept it wasn't clear yet, that the 2 use cases "argument match" and "invocation count" matcher are completely distinct. With that knowledge, we should really separate them.

A couple comments. Will add them in the diff.

[petergtz]

It looks like matcher_factories.go is not changed to use ArgumentMatcher. So that needs adjustment. BTW, instead of writing this file manually, there is internal/generate_matchers/matcher_generation.go.

As the comment there implies, you can run

go generate github.com/petergtz/pegomock/internal/generate_matchers

to generate all the default matchers. You should probably add your XThat functions there. Sorry, overlooked this in your previous PR, so I'd like to fill this back here, if that's okay with you.

[petergtz]

Nice! Thanks again, @yhrn.