92 lines
1.6 KiB
Rust
92 lines
1.6 KiB
Rust
fn main() {
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a();
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b();
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c();
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d();
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}
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fn a() {
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#[allow(dead_code)]
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union U {
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f1: u32,
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f2: f32,
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}
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let mut u = U { f1: 1 };
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unsafe {
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let b1 = &mut u.f1;
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*b1 = 5;
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}
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assert_eq!(unsafe { u.f1 }, 5);
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}
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fn b() {
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#[derive(Copy, Clone)]
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struct S {
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x: u32,
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y: u32,
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}
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#[allow(dead_code)]
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union U {
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s: S,
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both: u64,
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}
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let mut u = U { s: S { x: 1, y: 2 } };
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unsafe {
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let bx = &mut u.s.x;
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let by = &mut u.s.y;
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*bx = 5;
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*by = 10;
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}
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assert_eq!(unsafe { u.s.x }, 5);
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assert_eq!(unsafe { u.s.y }, 10);
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}
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fn c() {
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#[repr(u32)]
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enum Tag {
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I,
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F,
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}
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#[repr(C)]
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union U {
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i: i32,
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f: f32,
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}
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#[repr(C)]
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struct Value {
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tag: Tag,
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u: U,
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}
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fn is_zero(v: Value) -> bool {
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unsafe {
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match v {
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Value { tag: Tag::I, u: U { i: 0 } } => true,
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Value { tag: Tag::F, u: U { f } } => f == 0.0,
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_ => false,
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}
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}
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}
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assert!(is_zero(Value { tag: Tag::I, u: U { i: 0 } }));
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assert!(is_zero(Value { tag: Tag::F, u: U { f: 0.0 } }));
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assert!(!is_zero(Value { tag: Tag::I, u: U { i: 1 } }));
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assert!(!is_zero(Value { tag: Tag::F, u: U { f: 42.0 } }));
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}
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fn d() {
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union MyUnion {
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f1: u32,
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f2: f32,
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}
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let u = MyUnion { f1: 10 };
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unsafe {
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match u {
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MyUnion { f1: 10 } => {}
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MyUnion { f2: _f2 } => panic!("foo"),
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}
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}
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}
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