├── .github ├── FUNDING.yml └── workflows │ └── ci.yml ├── .gitignore ├── Cargo.toml ├── LICENSE-APACHE ├── LICENSE-MIT ├── README.md ├── src └── lib.rs └── tests └── test.rs /.github/FUNDING.yml: -------------------------------------------------------------------------------- 1 | github: dtolnay 2 | -------------------------------------------------------------------------------- /.github/workflows/ci.yml: -------------------------------------------------------------------------------- 1 | name: CI 2 | 3 | on: 4 | push: 5 | pull_request: 6 | workflow_dispatch: 7 | schedule: [cron: "40 1 * * *"] 8 | 9 | permissions: 10 | contents: read 11 | 12 | env: 13 | RUSTFLAGS: -Dwarnings 14 | 15 | jobs: 16 | pre_ci: 17 | uses: dtolnay/.github/.github/workflows/pre_ci.yml@master 18 | 19 | test: 20 | name: Rust ${{matrix.rust}} 21 | needs: pre_ci 22 | if: needs.pre_ci.outputs.continue 23 | runs-on: ubuntu-latest 24 | strategy: 25 | fail-fast: false 26 | matrix: 27 | rust: [nightly, beta, stable, 1.56.0] 28 | timeout-minutes: 45 29 | steps: 30 | - uses: actions/checkout@v4 31 | - uses: dtolnay/rust-toolchain@master 32 | with: 33 | toolchain: ${{matrix.rust}} 34 | - name: Enable type layout randomization 35 | run: echo RUSTFLAGS=${RUSTFLAGS}\ -Zrandomize-layout >> $GITHUB_ENV 36 | if: matrix.rust == 'nightly' 37 | - run: cargo test 38 | 39 | minimal: 40 | name: Minimal versions 41 | needs: pre_ci 42 | if: needs.pre_ci.outputs.continue 43 | runs-on: ubuntu-latest 44 | timeout-minutes: 45 45 | steps: 46 | - uses: actions/checkout@v4 47 | - uses: dtolnay/rust-toolchain@nightly 48 | - run: cargo generate-lockfile -Z minimal-versions 49 | - run: cargo check --locked 50 | 51 | doc: 52 | name: Documentation 53 | needs: pre_ci 54 | if: needs.pre_ci.outputs.continue 55 | runs-on: ubuntu-latest 56 | env: 57 | RUSTDOCFLAGS: -Dwarnings 58 | timeout-minutes: 45 59 | steps: 60 | - uses: actions/checkout@v4 61 | - uses: dtolnay/rust-toolchain@nightly 62 | - uses: dtolnay/install@cargo-docs-rs 63 | - run: cargo docs-rs 64 | 65 | clippy: 66 | name: Clippy 67 | runs-on: ubuntu-latest 68 | if: github.event_name != 'pull_request' 69 | timeout-minutes: 45 70 | steps: 71 | - uses: actions/checkout@v4 72 | - uses: dtolnay/rust-toolchain@clippy 73 | - run: cargo clippy --tests -- -Dclippy::all -Dclippy::pedantic 74 | 75 | miri: 76 | name: Miri 77 | needs: pre_ci 78 | if: needs.pre_ci.outputs.continue 79 | runs-on: ubuntu-latest 80 | timeout-minutes: 45 81 | steps: 82 | - uses: actions/checkout@v4 83 | - uses: dtolnay/rust-toolchain@miri 84 | with: 85 | toolchain: nightly-2025-05-16 # https://github.com/rust-lang/miri/issues/4323 86 | - run: cargo miri setup 87 | - run: cargo miri test 88 | env: 89 | MIRIFLAGS: -Zmiri-strict-provenance 90 | 91 | outdated: 92 | name: Outdated 93 | runs-on: ubuntu-latest 94 | if: github.event_name != 'pull_request' 95 | timeout-minutes: 45 96 | steps: 97 | - uses: actions/checkout@v4 98 | - uses: dtolnay/rust-toolchain@stable 99 | - uses: dtolnay/install@cargo-outdated 100 | - run: cargo outdated --exit-code 1 101 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | /Cargo.lock 2 | /target/ 3 | -------------------------------------------------------------------------------- /Cargo.toml: -------------------------------------------------------------------------------- 1 | [package] 2 | name = "erased-discriminant" 3 | version = "1.0.1" 4 | authors = ["David Tolnay "] 5 | categories = ["no-std"] 6 | description = "Type-erased version of core::mem::Discriminant" 7 | documentation = "https://docs.rs/erased-discriminant" 8 | edition = "2021" 9 | license = "MIT OR Apache-2.0" 10 | repository = "https://github.com/dtolnay/erased-discriminant" 11 | rust-version = "1.56" 12 | 13 | [dependencies] 14 | typeid = "1" 15 | 16 | [package.metadata.docs.rs] 17 | targets = ["x86_64-unknown-linux-gnu"] 18 | rustdoc-args = [ 19 | "--generate-link-to-definition", 20 | "--extern-html-root-url=core=https://doc.rust-lang.org", 21 | "--extern-html-root-url=alloc=https://doc.rust-lang.org", 22 | "--extern-html-root-url=std=https://doc.rust-lang.org", 23 | ] 24 | -------------------------------------------------------------------------------- /LICENSE-APACHE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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IN NO EVENT 19 | SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 20 | CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION 21 | OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR 22 | IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 23 | DEALINGS IN THE SOFTWARE. 24 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Type-erased `Discriminant` 2 | 3 | [github](https://github.com/dtolnay/erased-discriminant) 4 | [crates.io](https://crates.io/crates/erased-discriminant) 5 | [docs.rs](https://docs.rs/erased-discriminant) 6 | [build status](https://github.com/dtolnay/erased-discriminant/actions?query=branch%3Amaster) 7 | 8 | This crate provides a `Discriminant` type that behaves like 9 | `core::mem::Discriminant` but without the generic type parameter `T`. With 10 | this, we can build collections such as HashSet that contain discriminants from a 11 | mixture of different enum types. 12 | 13 | ```rust 14 | use erased_discriminant::Discriminant; 15 | use std::collections::HashSet; 16 | 17 | enum Enum { 18 | A(i32), 19 | B, 20 | } 21 | 22 | enum DifferentEnum { 23 | A, 24 | } 25 | 26 | let mut set = HashSet::new(); 27 | set.insert(Discriminant::of(&Enum::A(99))); 28 | set.insert(Discriminant::of(&Enum::B)); 29 | set.insert(Discriminant::of(&DifferentEnum::A)); 30 | assert_eq!(set.len(), 3); 31 | ``` 32 | 33 |
34 | 35 | #### License 36 | 37 | 38 | Licensed under either of Apache License, Version 39 | 2.0 or MIT license at your option. 40 | 41 | 42 |
43 | 44 | 45 | Unless you explicitly state otherwise, any contribution intentionally submitted 46 | for inclusion in this crate by you, as defined in the Apache-2.0 license, shall 47 | be dual licensed as above, without any additional terms or conditions. 48 | 49 | -------------------------------------------------------------------------------- /src/lib.rs: -------------------------------------------------------------------------------- 1 | //! [![github]](https://github.com/dtolnay/erased-discriminant) [![crates-io]](https://crates.io/crates/erased-discriminant) [![docs-rs]](https://docs.rs/erased-discriminant) 2 | //! 3 | //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github 4 | //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust 5 | //! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs 6 | //! 7 | //! This crate provides a `Discriminant` type that behaves like 8 | //! `core::mem::Discriminant` but without the generic type parameter `T`. 9 | //! With this, we can build collections such as HashSet that contain 10 | //! discriminants from a mixture of different enum types. 11 | //! 12 | //! ``` 13 | //! use erased_discriminant::Discriminant; 14 | //! use std::collections::HashSet; 15 | //! 16 | //! enum Enum { 17 | //! A(i32), 18 | //! B, 19 | //! } 20 | //! 21 | //! enum DifferentEnum { 22 | //! A, 23 | //! } 24 | //! 25 | //! let mut set = HashSet::new(); 26 | //! set.insert(Discriminant::of(&Enum::A(99))); 27 | //! set.insert(Discriminant::of(&Enum::B)); 28 | //! set.insert(Discriminant::of(&DifferentEnum::A)); 29 | //! assert_eq!(set.len(), 3); 30 | //! ``` 31 | 32 | #![no_std] 33 | #![doc(html_root_url = "https://docs.rs/erased-discriminant/1.0.1")] 34 | #![deny(unsafe_op_in_unsafe_fn)] 35 | #![allow(clippy::doc_markdown, clippy::missing_safety_doc)] 36 | 37 | extern crate alloc; 38 | 39 | use alloc::boxed::Box; 40 | use core::any::TypeId; 41 | use core::fmt::{self, Debug}; 42 | use core::hash::{Hash, Hasher}; 43 | use core::mem::{self, MaybeUninit}; 44 | 45 | /// A type-erased version of `core::mem::Discriminant`. 46 | pub struct Discriminant { 47 | data: MaybeUninit<*mut ()>, 48 | vtable: &'static DiscriminantVTable, 49 | } 50 | 51 | impl Discriminant { 52 | pub fn of(value: &T) -> Self { 53 | let discriminant = mem::discriminant(value); 54 | let data = if small_discriminant::() { 55 | let mut data = MaybeUninit::<*mut ()>::uninit(); 56 | unsafe { 57 | data.as_mut_ptr() 58 | .cast::>() 59 | .write(discriminant); 60 | } 61 | data 62 | } else { 63 | MaybeUninit::new(Box::into_raw(Box::new(discriminant)).cast::<()>()) 64 | }; 65 | Discriminant { 66 | data, 67 | vtable: &DiscriminantVTable { 68 | eq: discriminant_eq::, 69 | hash: discriminant_hash::, 70 | clone: discriminant_clone::, 71 | debug: discriminant_debug::, 72 | drop: discriminant_drop::, 73 | type_id: typeid::of::>, 74 | }, 75 | } 76 | } 77 | } 78 | 79 | fn small_discriminant() -> bool { 80 | mem::size_of::>() <= mem::size_of::<*const ()>() 81 | } 82 | 83 | struct DiscriminantVTable { 84 | eq: unsafe fn(this: &Discriminant, other: &Discriminant) -> bool, 85 | hash: unsafe fn(this: &Discriminant, hasher: &mut dyn Hasher), 86 | clone: unsafe fn(this: &Discriminant) -> Discriminant, 87 | debug: unsafe fn(this: &Discriminant, formatter: &mut fmt::Formatter) -> fmt::Result, 88 | drop: unsafe fn(this: &mut Discriminant), 89 | type_id: fn() -> TypeId, 90 | } 91 | 92 | unsafe fn as_ref(this: &Discriminant) -> &core::mem::Discriminant { 93 | unsafe { 94 | &*if small_discriminant::() { 95 | this.data.as_ptr().cast::>() 96 | } else { 97 | this.data.assume_init().cast::>() 98 | } 99 | } 100 | } 101 | 102 | unsafe fn discriminant_eq(this: &Discriminant, other: &Discriminant) -> bool { 103 | (other.vtable.type_id)() == typeid::of::>() 104 | && unsafe { as_ref::(this) } == unsafe { as_ref::(other) } 105 | } 106 | 107 | unsafe fn discriminant_hash(this: &Discriminant, mut hasher: &mut dyn Hasher) { 108 | typeid::of::>().hash(&mut hasher); 109 | unsafe { as_ref::(this) }.hash(&mut hasher); 110 | } 111 | 112 | unsafe fn discriminant_clone(this: &Discriminant) -> Discriminant { 113 | if small_discriminant::() { 114 | Discriminant { 115 | data: this.data, 116 | vtable: this.vtable, 117 | } 118 | } else { 119 | let discriminant = unsafe { *this.data.assume_init().cast::>() }; 120 | Discriminant { 121 | data: MaybeUninit::new(Box::into_raw(Box::new(discriminant)).cast::<()>()), 122 | vtable: this.vtable, 123 | } 124 | } 125 | } 126 | 127 | unsafe fn discriminant_debug( 128 | this: &Discriminant, 129 | formatter: &mut fmt::Formatter, 130 | ) -> fmt::Result { 131 | Debug::fmt(unsafe { as_ref::(this) }, formatter) 132 | } 133 | 134 | unsafe fn discriminant_drop(this: &mut Discriminant) { 135 | if !small_discriminant::() { 136 | let _ = 137 | unsafe { Box::from_raw(this.data.assume_init().cast::>()) }; 138 | } 139 | } 140 | 141 | impl Eq for Discriminant {} 142 | 143 | impl PartialEq for Discriminant { 144 | fn eq(&self, other: &Self) -> bool { 145 | unsafe { (self.vtable.eq)(self, other) } 146 | } 147 | } 148 | 149 | impl Hash for Discriminant { 150 | fn hash(&self, hasher: &mut H) { 151 | unsafe { (self.vtable.hash)(self, hasher) }; 152 | } 153 | } 154 | 155 | impl Clone for Discriminant { 156 | fn clone(&self) -> Self { 157 | unsafe { (self.vtable.clone)(self) } 158 | } 159 | } 160 | 161 | impl Debug for Discriminant { 162 | fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result { 163 | unsafe { (self.vtable.debug)(self, formatter) } 164 | } 165 | } 166 | 167 | impl Drop for Discriminant { 168 | fn drop(&mut self) { 169 | unsafe { (self.vtable.drop)(self) }; 170 | } 171 | } 172 | -------------------------------------------------------------------------------- /tests/test.rs: -------------------------------------------------------------------------------- 1 | use erased_discriminant::Discriminant; 2 | use std::collections::HashSet; 3 | 4 | enum Enum<'a> { 5 | A(#[allow(dead_code)] &'a str), 6 | B, 7 | } 8 | 9 | enum DifferentEnum { 10 | A, 11 | } 12 | 13 | #[test] 14 | fn test_eq() { 15 | let temporary_string = "...".to_owned(); 16 | let a = Enum::A(&temporary_string); 17 | let b = Enum::B; 18 | let a_discriminant = Discriminant::of(&a); 19 | let b_discriminant = Discriminant::of(&b); 20 | drop(temporary_string); 21 | assert_eq!(a_discriminant, a_discriminant); 22 | assert_ne!(a_discriminant, b_discriminant); 23 | 24 | let different_discriminant = Discriminant::of(&DifferentEnum::A); 25 | assert_ne!(a_discriminant, different_discriminant); 26 | assert_ne!(b_discriminant, different_discriminant); 27 | } 28 | 29 | #[test] 30 | fn test_hashset() { 31 | let mut set = HashSet::new(); 32 | 33 | let temporary_string = "...".to_owned(); 34 | set.insert(Discriminant::of(&Enum::A(&temporary_string))); 35 | set.insert(Discriminant::of(&Enum::B)); 36 | set.insert(Discriminant::of(&DifferentEnum::A)); 37 | drop(temporary_string); 38 | assert_eq!(set.len(), 3); 39 | 40 | set.insert(Discriminant::of(&Enum::A("other string"))); 41 | set.insert(Discriminant::of(&Enum::B)); 42 | set.insert(Discriminant::of(&DifferentEnum::A)); 43 | assert_eq!(set.len(), 3); 44 | 45 | assert_eq!(set, set.clone()); 46 | } 47 | --------------------------------------------------------------------------------