error[E0038]: the trait `AsyncFnMut` cannot be made into an object
  --> src/lib.rs:5:22
   |
5  | async fn foo(x: &dyn AsyncFn()) {
   |                      ^^^^^^^^^ `AsyncFnMut` cannot be made into an object
   |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/async_function.rs:30:10
   |
30 |     type CallRefFuture<'a>: Future<Output = Self::Output>
   |          ^^^^^^^^^^^^^ the trait cannot be made into an object because it contains the generic associated type `CallRefFuture`
   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFnMut` for this new enum and using it instead:
             &F
             &mut F
             std::boxed::Box<F, A>

error[E0038]: the trait `AsyncFn` cannot be made into an object
  --> src/lib.rs:5:18
   |
5  | async fn foo(x: &dyn AsyncFn()) {
   |                  ^^^^^^^^^^^^^ `AsyncFn` cannot be made into an object
   |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/async_function.rs:30:10
   |
30 |     type CallRefFuture<'a>: Future<Output = Self::Output>
   |          ^^^^^^^^^^^^^ the trait cannot be made into an object because it contains the generic associated type `CallRefFuture`
   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
             &F
             std::boxed::Box<F, A>

error[E0038]: the trait `AsyncFn` cannot be made into an object
  --> src/lib.rs:6:5
   |
6  |     x().await;
   |     ^^^ `AsyncFn` cannot be made into an object
   |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/async_function.rs:30:10
   |
30 |     type CallRefFuture<'a>: Future<Output = Self::Output>
   |          ^^^^^^^^^^^^^ the trait cannot be made into an object because it contains the generic associated type `CallRefFuture`
   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
             &F
             std::boxed::Box<F, A>

error[E0038]: the trait `AsyncFn` cannot be made into an object
  --> src/lib.rs:6:9
   |
6  |     x().await;
   |         ^^^^^ `AsyncFn` cannot be made into an object
   |
note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
  --> /playground/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/async_function.rs:30:10
   |
30 |     type CallRefFuture<'a>: Future<Output = Self::Output>
   |          ^^^^^^^^^^^^^ the trait cannot be made into an object because it contains the generic associated type `CallRefFuture`
   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `AsyncFn` for this new enum and using it instead:
             &F
             std::boxed::Box<F, A>

For more information about this error, try `rustc --explain E0038`.
error: could not compile `playground` (lib) due to 4 previous errors

error[E0038]: the trait `AsyncFn` cannot be made into an object
  --> src/lib.rs:5:22
   |
5  | async fn foo(x: &dyn AsyncFn()) {
   |                      ^^^^^^^^^ `AsyncFn` cannot be made into an object
   |
note: `async` closures are not yet usable with dynamic dispatch. See <link for more information>
error: could not compile `playground` (lib) due to 1 previous error