Convert number to enum

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.

Example

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); } 

Signature

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> { /* ... */ } } 

Discriminants

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).

License