1 error[E0277]: `Rc<RefCell<A>>` cannot be sent between threads safely
2 --> $DIR/issue-7013.rs:24:19
4 LL | let a = A {v: Box::new(B{v: None}) as Box<dyn Foo + Send>};
5 | ^^^^^^^^^^^^^^^^^^^^ `Rc<RefCell<A>>` cannot be sent between threads safely
7 = help: within `B`, the trait `Send` is not implemented for `Rc<RefCell<A>>`
8 = note: required because it appears within the type `Option<Rc<RefCell<A>>>`
9 note: required because it appears within the type `B`
10 --> $DIR/issue-7013.rs:8:8
14 = note: required for the cast from `B` to the object type `dyn Foo + Send`
16 error: aborting due to previous error
18 For more information about this error, try `rustc --explain E0277`.