31 lines
775 B
Rust
31 lines
775 B
Rust
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// run-pass
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#![allow(dead_code)]
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use std::mem::{size_of, transmute};
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union U1<A: Copy> {
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a: A,
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}
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union U2<A: Copy, B: Copy> {
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a: A,
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b: B,
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}
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fn main() {
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// Unions do not participate in niche-filling/non-zero optimization...
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assert!(size_of::<Option<U2<&u8, u8>>>() > size_of::<U2<&u8, u8>>());
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assert!(size_of::<Option<U2<&u8, ()>>>() > size_of::<U2<&u8, ()>>());
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// ...even when theoretically possible:
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assert!(size_of::<Option<U1<&u8>>>() > size_of::<U1<&u8>>());
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assert!(size_of::<Option<U2<&u8, &u8>>>() > size_of::<U2<&u8, &u8>>());
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// The unused bits of the () variant can have any value.
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let zeroed: U2<&u8, ()> = unsafe { transmute(std::ptr::null::<u8>()) };
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if let None = Some(zeroed) {
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panic!()
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}
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}
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