Pre-RFC: Sealed traits

[RustyYato]

I'll start a new thread here on internals, and we can flesh it out there.

This Pre-RFC (Take 2) is closed.

Here it is:

[Closed] Pre-RFC: Sealed Traits take 2

This is a brach off of Pre-RFC: Sealed traits, and has few new semantics and lots of new layout guarantees. NOTE This Pre-RFC is CLOSED Sealed Traits Motivation There is a large gap between traits and enums. Traits give you lots of freedom when developing an API, and make it really easy to extend the API to handle types that weren’t handled before, or let users implement it for their own types. Traits can also be dynamically dispatched which is allows for code to handle a variety of types tha…