commit | cbd0311724eb8382bda7efb20d2131be0ad835c4 | [log] [tgz] |
---|---|---|
author | Andrew Walbran <qwandor@google.com> | Thu Dec 02 11:49:30 2021 +0000 |
committer | Andrew Walbran <qwandor@google.com> | Wed Dec 08 12:25:11 2021 +0000 |
tree | 2df8e61d06b48bf2b93ef276e8e7d4bdb7f7ded3 | |
parent | fb5796063541e66beca5e32e77fde1e0c7368e58 [diff] |
Initial import enumn was previously included in crosvm, now they are using the crates.io crate instead so we need to import it into AOSP. Bug: 207770431 Bug: 209654193 Test: m crosvm Change-Id: Ic8a6ec3afa43811e54fa87d95d4f9eaaa58d9e2c
This crate provides a derive macro to generate a function for converting a primitive integer into the corresponding variant of an enum.
The generated function is named n
and has the following signature:
impl YourEnum { pub fn n(value: Repr) -> Option<Self>; }
where Repr
is an integer type of the right size as described in more detail below.
use enumn::N; #[derive(PartialEq, Debug, N)] enum Status { LegendaryTriumph, QualifiedSuccess, FortuitousRevival, IndeterminateStalemate, RecoverableSetback, DireMisadventure, AbjectFailure, } fn main() { let s = Status::n(1); assert_eq!(s, Some(Status::QualifiedSuccess)); let s = Status::n(9); assert_eq!(s, None); }
The generated signature depends on whether the enum has a #[repr(..)]
attribute. If a repr
is specified, the input to n
will be required to be of that type.
#[derive(enumn::N)] #[repr(u8)] enum E { /* ... */ } // expands to: impl E { pub fn n(value: u8) -> Option<Self> { /* ... */ } }
On the other hand if no repr
is specified then we get a signature that is generic over a variety of possible types.
impl E { pub fn n<REPR: Into<i64>>(value: REPR) -> Option<Self> { /* ... */ } }
The conversion respects explictly specified enum discriminants. Consider this enum:
#[derive(enumn::N)] enum Letter { A = 65, B = 66, }
Here Letter::n(65)
would return Some(Letter::A)
.