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