1 // compile-flags: -Z print-type-sizes
4 // ^-- needed because `--pass check` does not emit the output needed.
5 // FIXME: consider using an attribute instead of side-effects.
7 // This file illustrates how niche-filling enums are handled,
8 // modelled after cases like `Option<&u32>`, `Option<bool>` and such.
10 // It uses NonZeroU32 rather than `&_` or `Unique<_>`, because
11 // the test is not set up to deal with target-dependent pointer width.
13 // It avoids using u64/i64 because on some targets that is only 4-byte
14 // aligned (while on most it is 8-byte aligned) and so the resulting
15 // padding and overall computed sizes can be quite different.
20 use std::num::NonZeroU32;
22 pub enum MyOption<T> { None, Some(T) }
24 impl<T> Default for MyOption<T> {
25 fn default() -> Self { MyOption::None }
28 pub enum EmbeddedDiscr {
30 Record { pre: u8, val: NonZeroU32, post: u16 },
33 impl Default for EmbeddedDiscr {
34 fn default() -> Self { EmbeddedDiscr::None }
38 pub struct IndirectNonZero {
40 nested: NestedNonZero,
44 pub struct NestedNonZero {
50 impl Default for NestedNonZero {
51 fn default() -> Self {
52 NestedNonZero { pre: 0, val: NonZeroU32::new(1).unwrap(), post: 0 }
56 pub enum Enum4<A, B, C, D> {
63 pub union Union1<A: Copy> {
67 pub union Union2<A: Copy, B: Copy> {
73 fn start(_: isize, _: *const *const u8) -> isize {
74 let _x: MyOption<NonZeroU32> = Default::default();
75 let _y: EmbeddedDiscr = Default::default();
76 let _z: MyOption<IndirectNonZero> = Default::default();
77 let _a: MyOption<bool> = Default::default();
78 let _b: MyOption<char> = Default::default();
79 let _c: MyOption<std::cmp::Ordering> = Default::default();
80 let _b: MyOption<MyOption<u8>> = Default::default();
81 let _e: Enum4<(), char, (), ()> = Enum4::One(());
82 let _f: Enum4<(), (), bool, ()> = Enum4::One(());
83 let _g: Enum4<(), (), (), MyOption<u8>> = Enum4::One(());
85 // Unions do not currently participate in niche filling.
86 let _h: MyOption<Union2<NonZeroU32, u32>> = Default::default();
88 // ...even when theoretically possible.
89 let _i: MyOption<Union1<NonZeroU32>> = Default::default();
90 let _j: MyOption<Union2<NonZeroU32, NonZeroU32>> = Default::default();