rust/src/test/ui/union/union-deref.rs

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//! Test the part of RFC 2514 that is about not applying `DerefMut` coercions
//! of union fields.
#![feature(untagged_unions)]
use std::mem::ManuallyDrop;
union U1<T> { x:(), f: ManuallyDrop<(T,)> }
union U2<T> { x:(), f: (ManuallyDrop<(T,)>,) }
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fn main() {
let mut u : U1<Vec<i32>> = U1 { x: () };
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unsafe { (*u.f).0 = Vec::new() }; // explicit deref, this compiles
unsafe { u.f.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on union field
let mut u : U2<Vec<i32>> = U2 { x: () };
unsafe { (*u.f.0).0 = Vec::new() }; // explicit deref, this compiles
unsafe { u.f.0.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on union field
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}