Rust has unsized (aka dynamically-sized) types, trait objects and slices are probably the most commonly encountered DSTs.

There are two main limitations to them:

* by default most generic code can not operate over them, generics require the special `?Sized` bound to allow DSTs (essentially generics have a default Sized generic bound)

* Rust doesn't currently support dynamic stack allocation so DSTs can't be stack-allocated (https://github.com/rust-lang/rfcs/issues/618)