Proposal: allow Fut: ?Sized in Shared<Fut>

[TennyZhuang]

No description provided.

[taiki-e]

This is not possible in the current implementation because we are using enums to reduce memory usage. we could implement this by splitting the enum into multiple fields, but we prefer not to do it because it would increase memory usage. If the enum or union supports unsized values, this can be supported (rfcs: rust-lang/rfcs#1151, rust-lang/rfcs#3041).

futures-rs/futures-util/src/future/future/shared.rs

Lines 63 to 66 in e2cc747

	enum FutureOrOutput<Fut: Future> {
	Future(Fut),
	Output(Fut::Output),
	}