mirror of https://github.com/rust-lang/rust
98 lines
2.7 KiB
Rust
98 lines
2.7 KiB
Rust
//! This file illustrates how niche-filling enums are handled,
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//! modelled after cases like `Option<&u32>`, `Option<bool>` and such.
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//!
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//! It uses `NonZero<u32>` rather than `&_` or `Unique<_>`, because
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//! the test is not set up to deal with target-dependent pointer width.
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//!
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//! It avoids using `u64`/`i64` because on some targets that is only 4-byte
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//! aligned (while on most it is 8-byte aligned) and so the resulting
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//! padding and overall computed sizes can be quite different.
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//!
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//@ compile-flags: -Z print-type-sizes --crate-type lib
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//@ ignore-debug: debug assertions will print more types
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//@ build-pass
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//@ ignore-pass
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// ^-- needed because `--pass check` does not emit the output needed.
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// FIXME: consider using an attribute instead of side-effects.
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#![allow(dead_code)]
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#![feature(rustc_attrs)]
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use std::num::NonZero;
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pub enum MyOption<T> { None, Some(T) }
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#[rustc_layout_scalar_valid_range_start(0)]
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#[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
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pub struct MyNotNegativeOne {
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_i: i32,
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}
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impl<T> Default for MyOption<T> {
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fn default() -> Self { MyOption::None }
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}
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pub enum EmbeddedDiscr {
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None,
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Record { pre: u8, val: NonZero<u32>, post: u16 },
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}
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impl Default for EmbeddedDiscr {
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fn default() -> Self { EmbeddedDiscr::None }
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}
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#[derive(Default)]
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pub struct IndirectNonZero {
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pre: u8,
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nested: NestedNonZero,
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post: u16,
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}
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pub struct NestedNonZero {
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pre: u8,
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val: NonZero<u32>,
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post: u16,
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}
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impl Default for NestedNonZero {
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fn default() -> Self {
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NestedNonZero { pre: 0, val: unsafe { NonZero::new_unchecked(1) }, post: 0 }
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}
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}
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pub enum Enum4<A, B, C, D> {
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One(A),
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Two(B),
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Three(C),
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Four(D)
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}
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pub union Union1<A: Copy> {
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a: A,
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}
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pub union Union2<A: Copy, B: Copy> {
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a: A,
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b: B,
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}
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pub fn test() {
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let _x: MyOption<NonZero<u32>> = Default::default();
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let _y: EmbeddedDiscr = Default::default();
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let _z: MyOption<IndirectNonZero> = Default::default();
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let _a: MyOption<bool> = Default::default();
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let _b: MyOption<char> = Default::default();
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let _c: MyOption<std::cmp::Ordering> = Default::default();
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let _d: MyOption<MyOption<u8>> = Default::default();
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let _e: Enum4<(), char, (), ()> = Enum4::One(());
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let _f: Enum4<(), (), bool, ()> = Enum4::One(());
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let _g: Enum4<(), (), (), MyOption<u8>> = Enum4::One(());
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let _h: MyOption<MyNotNegativeOne> = Default::default();
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// Unions do not currently participate in niche filling.
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let _i: MyOption<Union2<NonZero<u32>, u32>> = Default::default();
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// ...even when theoretically possible.
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let _j: MyOption<Union1<NonZero<u32>>> = Default::default();
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let _k: MyOption<Union2<NonZero<u32>, NonZero<u32>>> = Default::default();
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}
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