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explain why REF_AS_USIZE is important

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Ralf Jung 2019-08-30 09:31:21 +02:00
parent cf574091fb
commit e7fed140a4
1 changed files with 3 additions and 0 deletions
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3
src/test/ui/consts/const-eval/ub-ref.rs
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@ -11,6 +11,9 @@ const UNALIGNED: &u16 = unsafe { mem::transmute(&[0u8; 4]) };
const NULL: &u16 = unsafe { mem::transmute(0usize) };
//~^ ERROR it is undefined behavior to use this value
// It is very important that we reject this: We do promote `&(4 * REF_AS_USIZE)`,
// but that would fail to compile; so we ended up breaking user code that would
// have worked fine had we not promoted.
const REF_AS_USIZE: usize = unsafe { mem::transmute(&0) };
//~^ ERROR it is undefined behavior to use this value