1 error[E0225]: only auto traits can be used as additional traits in a trait object
2 --> $DIR/E0225.rs:12:32
4 LL | let _: Box<std::io::Read + std::io::Write>;
5 | ^^^^^^^^^^^^^^ non-auto additional trait
7 error: aborting due to previous error
9 For more information about this error, try `rustc --explain E0225`.