Torturing Rustc by Emulating HKTs

I've been playing around with type mapping like this in a highly experimental crate. The ability to map, filter and reduce types is insanely powerful but it's tough to get ergonomic syntax.

https://docs.rs/tuplemagic/latest/tuplemagic/index.html

I also hit a funny compiler end-of-the road last month when I wanted to try out generic_const_exprs for my RFC8366 implementation:

  pub struct VoucherDetails<C>
    where
      C: CapacityConfig,
      [(); C::SERIAL_NUMBER_MAX]:,
      [(); C::MANUFACTURER_PRIVATE_MAX]:,
      [(); C::IDEVID_ISSUER_MAX]:,
      // <imagine a dozen more properties here>
      [(); C::NONCE_B64_MAX]:,
  { ... }

This was incredible, even as it rapidly outpaced my PL and mathematics knowledge.