111 lines
2.7 KiB
Markdown
111 lines
2.7 KiB
Markdown
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Convert number to enum
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======================
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[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/enumn-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/enumn)
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[<img alt="crates.io" src="https://img.shields.io/crates/v/enumn.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/enumn)
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[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-enumn-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/enumn)
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[<img alt="build status" src="https://img.shields.io/github/actions/workflow/status/dtolnay/enumn/ci.yml?branch=master&style=for-the-badge" height="20">](https://github.com/dtolnay/enumn/actions?query=branch%3Amaster)
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This crate provides a derive macro to generate a function for converting a
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primitive integer into the corresponding variant of an enum.
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The generated function is named `n` and has the following signature:
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```rust
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impl YourEnum {
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pub fn n(value: Repr) -> Option<Self>;
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}
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```
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where `Repr` is an integer type of the right size as described in more
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detail below.
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## Example
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```rust
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use enumn::N;
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#[derive(PartialEq, Debug, N)]
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enum Status {
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LegendaryTriumph,
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QualifiedSuccess,
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FortuitousRevival,
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IndeterminateStalemate,
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RecoverableSetback,
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DireMisadventure,
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AbjectFailure,
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}
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fn main() {
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let s = Status::n(1);
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assert_eq!(s, Some(Status::QualifiedSuccess));
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let s = Status::n(9);
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assert_eq!(s, None);
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}
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```
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## Signature
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The generated signature depends on whether the enum has a `#[repr(..)]`
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attribute. If a `repr` is specified, the input to `n` will be required to be
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of that type.
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```rust
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#[derive(enumn::N)]
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#[repr(u8)]
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enum E {
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/* ... */
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}
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// expands to:
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impl E {
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pub fn n(value: u8) -> Option<Self> {
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/* ... */
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}
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}
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```
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On the other hand if no `repr` is specified then we get a signature that is
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generic over a variety of possible types.
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```rust
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impl E {
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pub fn n<REPR: Into<i64>>(value: REPR) -> Option<Self> {
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/* ... */
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}
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}
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```
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## Discriminants
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The conversion respects explictly specified enum discriminants. Consider
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this enum:
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```rust
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#[derive(enumn::N)]
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enum Letter {
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A = 65,
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B = 66,
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}
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```
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Here `Letter::n(65)` would return `Some(Letter::A)`.
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<br>
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#### License
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<sup>
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Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
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2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
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</sup>
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<br>
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<sub>
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
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be dual licensed as above, without any additional terms or conditions.
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</sub>
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