mirror of https://github.com/rust-lang/rust
35 lines
930 B
Rust
35 lines
930 B
Rust
//@ run-pass
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#![feature(const_ptr_write)]
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#![feature(const_mut_refs)]
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// Or, equivalently: `MaybeUninit`.
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pub union BagOfBits<T: Copy> {
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uninit: (),
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_storage: T,
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}
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pub const fn make_1u8_bag<T: Copy>() -> BagOfBits<T> {
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assert!(core::mem::size_of::<T>() >= 1);
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let mut bag = BagOfBits { uninit: () };
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unsafe { (&mut bag as *mut _ as *mut u8).write(1); };
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bag
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}
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pub fn check_bag<T: Copy>(bag: &BagOfBits<T>) {
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let val = unsafe { (bag as *const _ as *const u8).read() };
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assert_eq!(val, 1);
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}
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fn main() {
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check_bag(&make_1u8_bag::<[usize; 1]>()); // Fine
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check_bag(&make_1u8_bag::<usize>()); // Fine
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const CONST_ARRAY_BAG: BagOfBits<[usize; 1]> = make_1u8_bag();
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check_bag(&CONST_ARRAY_BAG); // Fine.
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const CONST_USIZE_BAG: BagOfBits<usize> = make_1u8_bag();
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// Used to panic since CTFE would make the entire `BagOfBits<usize>` uninit
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check_bag(&CONST_USIZE_BAG);
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}
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