This is a work-in-progress prototype/proposal for deduping a list of types. The primary motivation of this proposal is to reduce compile times when we need to deduplicate a large number of types.

This problem comes up a lot in practice and non-compiler metaprogramming counterpart solution become painfully slow for large number of types, often resorting to O(N) instantiations.

For data points, I have seen compilation units with metaprogramming constructs attempting to dedup ~5000 types. A single deduplication contributes to a whopping 20% of compile time of such compilation units.

TODO: Add tests.
TODO: Add docs.
TODO: Add correct diagnostics for bad usage.