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//! [![Rust](https://github.com/boltlabs-inc/vesta/actions/workflows/rust.yml/badge.svg)](https://github.com/boltlabs-inc/vesta/actions/workflows/rust.yml) //! ![license: MIT](https://img.shields.io/github/license/boltlabs-inc/vesta) //! [![crates.io](https://img.shields.io/crates/v/vesta)](https://crates.io/crates/vesta) //! [![docs.rs documentation](https://docs.rs/vesta/badge.svg)](https://docs.rs/vesta) //! //! > A **vesta**, otherwise known as a *match case*, is a small container for matches, named //! > after the Roman goddess of the hearth. //! > //! > **Vesta** is a crate for extensibly *matching cases* in Rust. //! //! By implementing [`Match`](Match@trait) and [`Case`] for some type (or better yet, correctly //! deriving them using the [`Match`](Match@macro) derive macro), you can pattern-match on that type //! using the [`case!`] macro almost like using the `match` keyword built into Rust. //! //! However, Vesta's [`case!`] macro is more general than `match`, because [`Match`] and [`Case`] //! are traits! This means you can enable pattern-matching for types which are not literally //! implemented as `enum`s, and you can write code which is generic over any type that is //! pattern-matchable. #![warn(missing_docs)] #![warn(missing_copy_implementations, missing_debug_implementations)] #![warn(unused_qualifications, unused_results)] #![warn(future_incompatible)] #![warn(unused)] // Documentation configuration #![forbid(broken_intra_doc_links)] pub use vesta_macro::{case, Match}; /// This module is exported so that the `derive_match!` macro can make reference to `vesta` itself /// from within the crate. #[doc(hidden)] pub mod vesta { pub use super::*; } /// A type which is [`Match`] can be pattern-matched using the [`case!`] macro and the methods of /// [`CaseExt`]/[`Case`]. /// /// In order for a type to be matched, it must implement [`Match`], as well as [`Case`] for each /// distinct case it can be matched against. pub unsafe trait Match: Sized { /// The range of [`tag`](Match::tag) for this type: either [`Nonexhaustive`], or /// [`Exhaustive<N>`](Exhaustive) for some `N`. /// /// No other types are permissible for this associated type; it is constrained by the sealed /// `Range` trait, which is only implemented for these two options. /// /// # Safety /// /// If the [`Range`](Match::Range) is [`Exhaustive<N>`](Exhaustive), then [`tag`](Match::tag) /// must *never* return `None`. For all `Some(m)` it returns, `m` must be *strictly less than* /// `N`. Undefined behavior may result if this guarantee is violated. type Range: sealed::Range; /// The tag of this value. /// /// # Safety /// /// If this function returns `Some(n)`, this is a *guarantee* that it is safe to call /// [`case`](Case::case) for this value at the type level tag `N = n`. It is undefined behavior /// for this function to return `Some(n)` if `<Self as Case<N>>::case(self)` would be unsafe. /// /// If the [`Range`](Match::Range) is [`Exhaustive<N>`](Exhaustive), then this function must /// *never* return `None`. For all `Some(m)` it returns, `m` must be *strictly less than* `N`. /// Undefined behavior may result if this guarantee is violated. /// /// Only if the [`Range`](Match::Range) is [`Nonexhaustive`] is it safe for this function to /// return `None`. Returning `None` will cause all pattern matches on this value to take the /// default case. /// /// This function should always return the same result. In general, it is impossible to safely /// implement [`Match`] for types with interior mutability, unless that interior mutability has /// no ability to change the tag. When pattern-matching occurs, there is no guarantee that /// `self.tag()` is checked and `self.case()` subsequently called (if applicable) in a single /// atomic action, which may lead to undefined behavior if the tag changes between these two /// moments. /// /// # Examples /// /// ``` /// use vesta::Match; /// /// assert_eq!(Some(0), None::<bool>.tag()); /// assert_eq!(Some(1), Some(true).tag()); /// ``` fn tag(&self) -> Option<usize>; } /// An extension trait providing methods analogous to those in [`Case`], but which take `self` and /// type parameters.<br>💡 Prefer using these to directly calling the methods in [`Case`]. pub trait CaseExt: Sized { /// If the value's [`tag`](Match::tag) is `N`, return that case. /// /// # Safety /// /// It is undefined behavior to call this function when [`self.tag()`](Match::tag) would return /// anything other than `Some(n)`, where `n = N`. /// /// # Examples /// /// ``` /// use vesta::{Match, CaseExt}; /// /// let option = Some("hello"); /// assert_eq!(option.tag(), Some(1)); /// let string = unsafe { option.case::<1>() }; /// assert_eq!(string, "hello"); /// ``` #[inline(always)] unsafe fn case<const N: usize>(self) -> Self::Case where Self: Case<N>, { Case::case(self) } /// If the value's [`tag`](Match::tag) is `N`, return that case; otherwise, return `self`. /// /// # Examples /// /// ``` /// use vesta::CaseExt; /// /// let result = Some("hello").try_case::<1>(); /// assert_eq!(result, Ok("hello")); /// ``` #[inline(always)] fn try_case<const N: usize>(self) -> Result<Self::Case, Self> where Self: Case<N>, { Case::try_case(self) } /// The inverse of [`case`](CaseExt::case): inject this case back into the matched type. /// /// This operation must not panic or otherwise fail. /// /// # Examples /// /// ``` /// use vesta::CaseExt; /// /// let option: Option<_> = "hello".uncase::<_, 1>(); /// assert_eq!(option, Some("hello")); /// ``` #[inline(always)] fn uncase<T, const N: usize>(self) -> T where T: Case<N, Case = Self>, { Case::uncase(self) } } impl<T: Sized> CaseExt for T {} /// Statically assert that the type of the given value is exhaustive for `N`. /// /// This function can only be called if `Self: Match<Range = Exhaustive<N>>`. It does nothing /// when called. /// /// # Examples /// /// ``` /// vesta::assert_exhaustive::<_, 2>(&Some(true)); /// ``` #[inline(always)] pub fn assert_exhaustive<T, const N: usize>(_: &T) where T: Match<Range = Exhaustive<N>>, { } /// Mark an unreachable location in generated code. /// /// # Panics /// /// In debug mode, panics immediately when this function is called. /// /// # Safety /// /// In release mode, undefined behavior may occur if this function is ever called. #[doc(hidden)] #[inline(always)] pub unsafe fn unreachable<T>() -> T { #[cfg(release)] { core::hint::unreachable_unchecked() } #[cfg(not(release))] { core::unreachable!("invariant violation in `vesta::Match` or `vesta::Case` implementation") } } /// A marker type indicating that the [`tag`](Match::tag) for some type will always be *strictly /// less than* `N`. /// /// Use this to mark the [`Range`](Match::Range) of exhaustive enumerations. #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)] pub enum Exhaustive<const N: usize> {} /// A marker type indicating that the [`tag`](Match::tag) for some type is not fixed to some known /// upper bound. /// /// Use this to mark the [`Range`](Match::Range) of non-exhaustive enumerations. #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)] pub enum Nonexhaustive {} /// An implementation of [`Case`] defines a particular case of a pattern match for a type.<br> ℹ️ /// Prefer using the methods of [`CaseExt`] to directly calling these methods. pub trait Case<const N: usize>: Match { /// The type of the data contained in the `N`th case of the matched type. type Case; /// If the value's [`tag`](Match::tag) is `N`, return that case. /// /// # Safety /// /// It is undefined behavior to call this function when [`self.tag()`](Match::tag) would return /// anything other than `Some(n)`, where `n = N`. /// /// # Examples /// /// ``` /// use vesta::{Match, Case}; /// /// let option = Some("hello"); /// assert_eq!(option.tag(), Some(1)); /// let string = unsafe { <_ as Case<1>>::case(option) }; /// assert_eq!(string, "hello"); /// ``` unsafe fn case(this: Self) -> Self::Case; /// If the value's [`tag`](Match::tag) is `N`, return that case; otherwise, return `self`. /// /// In its default implementation, this method checks that `self.tag() == N` and then calls /// [`case`](Case::case) only if so. /// /// In the case where this method can be more efficiently implemented than the composition of /// [`tag`](Match::tag) with [`case`](Case::case), this method can be overloaded. /// /// # Examples /// /// ``` /// use vesta::Case; /// /// let result = <_ as Case<1>>::try_case(Some("hello")); /// assert_eq!(result, Ok("hello")); /// ``` fn try_case(this: Self) -> Result<Self::Case, Self> { if this.tag() == Some(N) { // It is safe to call `self.case()` because we have checked the tag Ok(unsafe { Case::case(this) }) } else { Err(this) } } /// The inverse of [`case`](Case::case): inject this case back into the matched type. /// /// This operation must not panic or otherwise fail. /// /// # Examples /// /// ``` /// use vesta::Case; /// /// let option: Option<_> = <_ as Case<1>>::uncase("hello"); /// assert_eq!(option, Some("hello")); /// ``` fn uncase(case: Self::Case) -> Self; } mod sealed { pub trait Range {} impl<const N: usize> Range for super::Exhaustive<N> {} impl Range for super::Nonexhaustive {} } mod impls;