How do you actually use dynamically sized types in Rust?

Question

In theory, Dynamically-Sized Types (DST) have landed and we should now be able to use dynamically sized type instances. Practically speaking, I can neither make it work, nor

Answer 1

At the moment, to create a HasFoo storing a type-erased Foo you need to first create one with a fixed concrete type and then coerce a pointer to it to the DST form, that is

let has_too: &HasFoo = &HasFoo { f: Bar };

Calling has_foo.f.foo() then does what you expect.

In future these DST casts will almost certainly be possible with as, but for the moment coercion via an explicit type hint is required.