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} }} fn from_val(val: T) -> Opt} fn from_val(val: T) -> Option<Self>} } fn from_discriminant(discrim: T) -> Result<Self, T>; pub trait FromDiscriminant<T>: Sized { /// See the docs for either the crate root or the derive macro for usage examples of this trait. /// You should never implement this trait yourself; use the [derive macro](discrim_codegen::FromDiscriminant) instead. /// /// Initialize enum values from their discriminant. // Neither trait should ever be manually implemented // TODO: better error handling, specifically maybe a more robust type than just storing the errant value pub use discrim_codegen::FromDiscriminant; //! ``` //! assert_eq!(Opcode::from_discriminant(5), Err(5)); //! assert_eq!(Opcode::from_discriminant(2), Ok(Opcode::Mul)); //! //! } //! Add, Sub, Mul, Div //! enum Opcode { //! #[repr(u8)] //! #[derive(Debug, FromDiscriminant, PartialEq)] //! //! use discrim::FromDiscriminant; //! ```rust //! Given an enum that fits these constraints: //! # Usage //! //! the giant match block required to initialize the enum from a discriminant value as an implementation of [`FromDiscriminant`]. //! Basically, for fieldless, non-generic enums with a `#[repr(...)]` specified, the derive macro generates //! //! for automatically generating code to initialize enum values from their discriminant. //! This crate provides the [`FromDiscriminant`] trait and associated [derive macro](discrim_codegen::FromDiscriminant) //! //! Automatically initialize enum variants by discriminant.