unsized

By the same token, watercolours (which are pretty much universally regarded as paints) do soak into unsized papers.

Now in practice, if you encounter a type with an unsized type parameter, it's probably a smart pointer.

The unsized coercion you're thinking of is for converting trait object references to unsized trait object references; here we're talking about a field behind a reference.

In my understanding, Ada allows you to return unsized values, but it's generally implemented via a secondary stack.

It is really just a hack that reinterpretes the (vtable, ptr) of an unsized type as (len, ptr).

My understanding is that `async fn` in a trait is desugared to `fn() -> impl Future` just like it would be anywhere else, so there's no unsized types involved.

Every place there's an unsized array, something has to figure out how big it is and pass that info around.

And any pointer in Rust that targets an unsized type grows an additional metadata field (for trait objects, a vtable pointer).

I hope Rust will eventually make this kind of stuff easier (the nightly-only coerce-unsized would make that happen).

We are getting more and more MIR optimizations and without a semantics, the interactions of unsized locals with those optimizations are basically unpredictable.

You need to understand ownership, references, and unsized types.

You could ditch the concept of unsized types.

In Rust, trait objects are "unsized", which means they can only exist behind some kind of pointer.

Objects of type `Send` are "unsized" and must be held behind a pointer (which becomes a fat pointer).

It's like "I want a shared, immutable reference to something recursive, or unsized".

I'm sure that Ralf Jung would be happy to talk more about this if anyone has any ideas for how to move forward: "With #111374, unsized locals are no longer blatantly unsound.

Unsized locals are the only part of MIR that doesn't even have a proposed semantics that could be implemented in Miri.