error: future cannot be sent between threads safely --> $DIR/issue-70818.rs:4:38 | LL | fn foo(ty: T, ty1: U) -> impl Future + Send { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ future created by async block is not `Send` | note: captured value is not `Send` --> $DIR/issue-70818.rs:6:18 | LL | async { (ty, ty1) } | ^^^ has type `U` which is not `Send` help: consider restricting type parameter `U` | LL | fn foo(ty: T, ty1: U) -> impl Future + Send { | +++++++++++++++++++ error: aborting due to 1 previous error