Consider adding a contant-length permutation type

[chrisbouchard]

Hi there. I just discovered your library and it's exactly what I wanted for a little project I'm working on. So thank you!

One thought I had is, now that const generics are stable, would you consider adding a constant-length permutation type? (Possibly behind a feature flag?) The project I'm working on uses const generics and arrays heavily, and it would be very cool to have a permutation that is statically-guaranteed to be the right length for an array.

[starblue]

Hi, do you want to review the pull request #2 ?

The constant-length permutations are mutatis mutandis a copy of the existing permutations. I don't think you can do much better, because the n argument is removed for most methods.

I made Permutations generic over the two permutation types by just requiring that they implement TryFrom.

[chrisbouchard]

I got to thinking about that last night after I opened this issue. I threw together a playground with a proof-of-concept for a way to avoid repeating so much of the code between Permutation and ConstPermutation. What do you think?

[chrisbouchard]

Ok, I have an updated playground that also avoids repetition in the constructors by moving the main logic into private methods on PermutationBase. Like I say in the comment, I bet we could do this for permute as well but I haven't thought it through.