use std::mem::ManuallyDrop; #[derive(Clone)] //~ ERROR the trait bound `U1: Copy` is not satisfied union U1 { a: u8, } #[derive(Clone)] union U2 { a: u8, // OK } impl Copy for U2 {} #[derive(Clone, Copy)] union U3 { a: u8, // OK } #[derive(Clone, Copy)] union U4 { a: T, // OK } #[derive(Clone, Copy)] union U5 { a: ManuallyDrop, // OK } #[derive(Clone)] struct CloneNoCopy; fn main() { let u = U5 { a: ManuallyDrop::new(CloneNoCopy) }; let w = u.clone(); //~ ERROR the method }