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//! Module that holds Coproduct data structures, traits, and implementations //! //! Think of "Coproduct" as ad-hoc enums; allowing you to do something like this //! //! ``` //! #[macro_use] //! extern crate frunk; //! //! # fn main() { //! // For simplicity, assign our Coproduct type to a type alias //! // This is purely optional. //! type I32Bool = Coprod!(i32, bool); //! // Inject things into our Coproduct type //! let co1 = I32Bool::inject(3); //! let co2 = I32Bool::inject(true); //! //! // Getting stuff //! let get_from_1a: Option<&i32> = co1.get(); //! let get_from_1b: Option<&bool> = co1.get(); //! assert_eq!(get_from_1a, Some(&3)); //! assert_eq!(get_from_1b, None); //! //! let get_from_2a: Option<&i32> = co2.get(); //! let get_from_2b: Option<&bool> = co2.get(); //! assert_eq!(get_from_2a, None); //! assert_eq!(get_from_2b, Some(&true)); //! //! // *Taking* stuff (by value) //! let take_from_1a: Option<i32> = co1.take(); //! assert_eq!(take_from_1a, Some(3)); //! //! // Or with a Result //! let uninject_from_1a: Result<i32, _> = co1.uninject(); //! let uninject_from_1b: Result<bool, _> = co1.uninject(); //! assert_eq!(uninject_from_1a, Ok(3)); //! assert!(uninject_from_1b.is_err()); //! # } //! ``` //! //! Or, if you want to "fold" over all possible values of a coproduct //! //! ``` //! # #[macro_use] extern crate frunk; //! # fn main() { //! # type I32Bool = Coprod!(i32, bool); //! # let co1 = I32Bool::inject(3); //! # let co2 = I32Bool::inject(true); //! // In the below, we use unreachable!() to make it obvious hat we know what type of //! // item is inside our coproducts co1 and co2 but in real life, you should be writing //! // complete functions for all the cases when folding coproducts //! // //! // to_ref borrows every item so that we can fold without consuming the coproduct. //! assert_eq!( //! co1.to_ref().fold(hlist![|&i| format!("i32 {}", i), //! |&b| unreachable!() /* we know this won't happen for co1 */ ]), //! "i32 3".to_string()); //! assert_eq!( //! co2.to_ref().fold(hlist![|&i| unreachable!() /* we know this won't happen for co2 */, //! |&b| String::from(if b { "t" } else { "f" })]), //! "t".to_string()); //! //! // Here, we use the poly_fn! macro to declare a polymorphic function to avoid caring //! // about the order in which declare handlers for the types in our coproduct //! let folded = co1.fold( //! poly_fn![ //! |_b: bool| -> String { unreachable!() }, /* we know this won't happen for co1 */ //! |i: i32 | -> String { format!("i32 {}", i) }, //! ] //! ); //! assert_eq!(folded, "i32 3".to_string()); //! # } //! ``` use hlist::{HCons, HNil}; use indices::{Here, There}; use traits::{Func, Poly, ToMut, ToRef}; /// Enum type representing a Coproduct. Think of this as a Result, but capable /// of supporting any arbitrary number of types instead of just 2. /// /// To construct a Coproduct, you would typically declare a type using the `Coprod!` type /// macro and then use the `inject` method. /// /// # Examples /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32Bool = Coprod!(i32, bool); /// let co1 = I32Bool::inject(3); /// let get_from_1a: Option<&i32> = co1.get(); /// let get_from_1b: Option<&bool> = co1.get(); /// assert_eq!(get_from_1a, Some(&3)); /// assert_eq!(get_from_1b, None); /// # } /// ``` #[derive(PartialEq, Debug, Eq, Clone, Copy, PartialOrd, Ord, Hash)] #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] pub enum Coproduct<H, T> { /// Coproduct is either H or T, in this case, it is H Inl(H), /// Coproduct is either H or T, in this case, it is T Inr(T), } /// Phantom type for signature purposes only (has no value) /// /// Used by the macro to terminate the Coproduct type signature #[derive(PartialEq, Debug, Eq, Clone, Copy, PartialOrd, Ord, Hash)] #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))] pub enum CNil {} // Inherent methods impl<Head, Tail> Coproduct<Head, Tail> { /// Instantiate a coproduct from an element. /// /// This is generally much nicer than nested usage of `Coproduct::{Inl, Inr}`. /// The method uses a trick with type inference to automatically build the correct variant /// according to the input type. /// /// In standard usage, the `Index` type parameter can be ignored, /// as it will typically be solved for using type inference. /// /// # Rules /// /// If the type does not appear in the coproduct, the conversion is forbidden. /// /// If the type appears multiple times in the coproduct, type inference will fail. /// /// # Example /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// use frunk::Coproduct; /// /// type I32F32 = Coprod!(i32, f32); /// /// // Constructing coproducts using inject: /// let co1_nice: I32F32 = Coproduct::inject(1i32); /// let co2_nice: I32F32 = Coproduct::inject(42f32); /// /// // Compare this to the "hard way": /// let co1_ugly: I32F32 = Coproduct::Inl(1i32); /// let co2_ugly: I32F32 = Coproduct::Inr(Coproduct::Inl(42f32)); /// /// assert_eq!(co1_nice, co1_ugly); /// assert_eq!(co2_nice, co2_ugly); /// /// // Feel free to use `inject` on a type alias, or even directly on the /// // `Coprod!` macro. (the latter requires wrapping the type in `<>`) /// let _ = I32F32::inject(42f32); /// let _ = <Coprod!(i32, f32)>::inject(42f32); /// /// // You can also use a turbofish to specify the type of the input when /// // it is ambiguous (e.g. an empty `vec![]`). /// // The Index parameter should be left as `_`. /// type Vi32Vf32 = Coprod!(Vec<i32>, Vec<f32>); /// let _: Vi32Vf32 = Coproduct::inject::<Vec<i32>, _>(vec![]); /// # } /// ``` #[inline(always)] pub fn inject<T, Index>(to_insert: T) -> Self where Self: CoprodInjector<T, Index>, { CoprodInjector::inject(to_insert) } /// Borrow an element from a coproduct by type. /// /// # Example /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32F32 = Coprod!(i32, f32); /// /// // You can let type inference find the desired type: /// let co1 = I32F32::inject(42f32); /// let co1_as_i32: Option<&i32> = co1.get(); /// let co1_as_f32: Option<&f32> = co1.get(); /// assert_eq!(co1_as_i32, None); /// assert_eq!(co1_as_f32, Some(&42f32)); /// /// // You can also use turbofish syntax to specify the type. /// // The Index parameter should be left as `_`. /// let co2 = I32F32::inject(1i32); /// assert_eq!(co2.get::<i32, _>(), Some(&1)); /// assert_eq!(co2.get::<f32, _>(), None); /// # } /// ``` #[inline(always)] pub fn get<S, Index>(&self) -> Option<&S> where Self: CoproductSelector<S, Index>, { CoproductSelector::get(self) } /// Retrieve an element from a coproduct by type, ignoring all others. /// /// # Example /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32F32 = Coprod!(i32, f32); /// /// // You can let type inference find the desired type: /// let co1 = I32F32::inject(42f32); /// let co1_as_i32: Option<i32> = co1.take(); /// let co1_as_f32: Option<f32> = co1.take(); /// assert_eq!(co1_as_i32, None); /// assert_eq!(co1_as_f32, Some(42f32)); /// /// // You can also use turbofish syntax to specify the type. /// // The Index parameter should be left as `_`. /// let co2 = I32F32::inject(1i32); /// assert_eq!(co2.take::<i32, _>(), Some(1)); /// assert_eq!(co2.take::<f32, _>(), None); /// # } /// ``` #[inline(always)] pub fn take<T, Index>(self) -> Option<T> where Self: CoproductTaker<T, Index>, { CoproductTaker::take(self) } /// Attempt to extract a value from a coproduct (or get the remaining possibilities). /// /// By chaining calls to this, one can exhaustively match all variants of a coproduct. /// /// # Examples /// /// Basic usage: /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32F32 = Coprod!(i32, f32); /// type I32 = Coprod!(i32); // remainder after uninjecting f32 /// type F32 = Coprod!(f32); // remainder after uninjecting i32 /// /// let co1 = I32F32::inject(42f32); /// /// // You can let type inference find the desired type. /// let co1 = I32F32::inject(42f32); /// let co1_as_i32: Result<i32, F32> = co1.uninject(); /// let co1_as_f32: Result<f32, I32> = co1.uninject(); /// assert_eq!(co1_as_i32, Err(F32::inject(42f32))); /// assert_eq!(co1_as_f32, Ok(42f32)); /// /// // It is not necessary to annotate the type of the remainder: /// let res: Result<i32, _> = co1.uninject(); /// assert!(res.is_err()); /// /// // You can also use turbofish syntax to specify the type. /// // The Index parameter should be left as `_`. /// let co2 = I32F32::inject(1i32); /// assert_eq!(co2.uninject::<i32, _>(), Ok(1)); /// assert_eq!(co2.uninject::<f32, _>(), Err(I32::inject(1))); /// # } /// ``` /// /// Chaining calls for an exhaustive match: /// /// ```rust /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32F32 = Coprod!(i32, f32); /// /// // Be aware that this particular example could be /// // written far more succinctly using `fold`. /// fn handle_i32_f32(co: I32F32) -> &'static str { /// // Remove i32 from the coproduct /// let co = match co.uninject::<i32, _>() { /// Ok(x) => return "integer!", /// Err(co) => co, /// }; /// /// // Remove f32 from the coproduct /// let co = match co.uninject::<f32, _>() { /// Ok(x) => return "float!", /// Err(co) => co, /// }; /// /// // Now co is empty /// match co { /* unreachable */ } /// } /// /// assert_eq!(handle_i32_f32(I32F32::inject(3)), "integer!"); /// assert_eq!(handle_i32_f32(I32F32::inject(3.0)), "float!"); /// # } #[inline(always)] pub fn uninject<T, Index>(self) -> Result<T, <Self as CoprodUninjector<T, Index>>::Remainder> where Self: CoprodUninjector<T, Index>, { CoprodUninjector::uninject(self) } /// Extract a subset of the possible types in a coproduct (or get the remaining possibilities) /// /// This is basically [`uninject`] on steroids. It lets you remove a number /// of types from a coproduct at once, leaving behind the remainder in an `Err`. /// For instance, one can extract `Coprod!(C, A)` from `Coprod!(A, B, C, D)` /// to produce `Result<Coprod!(C, A), Coprod!(B, D)>`. /// /// Each type in the extracted subset is required to be part of the input coproduct. /// /// [`uninject`]: #method.uninject /// /// # Example /// /// Basic usage: /// /// ``` /// # #[macro_use] extern crate frunk; /// use ::frunk::Coproduct; /// /// # fn main() { /// type I32BoolF32 = Coprod!(i32, bool, f32); /// type I32F32 = Coprod!(i32, f32); /// /// let co1 = I32BoolF32::inject(42_f32); /// let co2 = I32BoolF32::inject(true); /// /// let sub1: Result<Coprod!(i32, f32), _> = co1.subset(); /// let sub2: Result<Coprod!(i32, f32), _> = co2.subset(); /// assert!(sub1.is_ok()); /// assert!(sub2.is_err()); /// /// // Turbofish syntax for specifying the target subset is also supported. /// // The Indices parameter should be left to type inference using `_`. /// assert!(co1.subset::<Coprod!(i32, f32), _>().is_ok()); /// assert!(co2.subset::<Coprod!(i32, f32), _>().is_err()); /// /// // Order doesn't matter. /// assert!(co1.subset::<Coprod!(f32, i32), _>().is_ok()); /// # } /// ``` /// /// Like `uninject`, `subset` can be used for exhaustive matching, /// with the advantage that it can remove more than one type at a time: /// /// ``` /// # #[macro_use] extern crate frunk; /// use frunk::Coproduct; /// /// # fn main() { /// fn handle_stringly_things(co: Coprod!(&'static str, String)) -> String { /// co.fold(hlist![ /// |s| format!("&str {}", s), /// |s| format!("String {}", s), /// ]) /// } /// /// fn handle_countly_things(co: Coprod!(u32)) -> String { /// co.fold(hlist![ /// |n| vec!["."; n as usize].concat(), /// ]) /// } /// /// fn handle_all(co: Coprod!(String, u32, &'static str)) -> String { /// // co is currently Coprod!(String, u32, &'static str) /// let co = match co.subset().map(handle_stringly_things) { /// Ok(s) => return s, /// Err(co) => co, /// }; /// /// // Now co is Coprod!(u32). /// let co = match co.subset().map(handle_countly_things) { /// Ok(s) => return s, /// Err(co) => co, /// }; /// /// // Now co is empty. /// match co { /* unreachable */ } /// } /// /// assert_eq!(handle_all(Coproduct::inject("hello")), "&str hello"); /// assert_eq!(handle_all(Coproduct::inject(String::from("World!"))), "String World!"); /// assert_eq!(handle_all(Coproduct::inject(4)), "...."); /// # } /// ``` #[inline(always)] pub fn subset<Targets, Indices>( self, ) -> Result<Targets, <Self as CoproductSubsetter<Targets, Indices>>::Remainder> where Self: CoproductSubsetter<Targets, Indices>, { CoproductSubsetter::subset(self) } /// Convert a coproduct into another that can hold its variants. /// /// This converts a coproduct into another one which is capable of holding each /// of its types. The most well-supported use-cases (i.e. those where type inference /// is capable of solving for the indices) are: /// /// * Reordering variants: `Coprod!(C, A, B) -> Coprod!(A, B, C)` /// * Embedding into a superset: `Coprod!(B, D) -> Coprod!(A, B, C, D, E)` /// * Coalescing duplicate inputs: `Coprod!(B, B, B, B) -> Coprod!(A, B, C)` /// /// and of course any combination thereof. /// /// # Rules /// /// If any type in the input does not appear in the output, the conversion is forbidden. /// /// If any type in the input appears multiple times in the output, type inference will fail. /// /// All of these rules fall naturally out of its fairly simple definition, /// which is equivalent to: /// /// ```text /// coprod.fold(hlist![ /// |x| Coproduct::inject(x), /// |x| Coproduct::inject(x), /// ... /// |x| Coproduct::inject(x), /// ]) /// ``` /// /// # Example /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32BoolF32 = Coprod!(i32, bool, f32); /// type BoolI32 = Coprod!(bool, i32); /// /// let co = BoolI32::inject(true); /// let embedded: I32BoolF32 = co.embed(); /// assert_eq!(embedded, I32BoolF32::inject(true)); /// /// // Turbofish syntax for specifying the output type is also supported. /// // The Indices parameter should be left to type inference using `_`. /// let embedded = co.embed::<I32BoolF32, _>(); /// assert_eq!(embedded, I32BoolF32::inject(true)); /// # } /// ``` #[inline(always)] pub fn embed<Targets, Indices>(self) -> Targets where Self: CoproductEmbedder<Targets, Indices>, { CoproductEmbedder::embed(self) } /// Borrow each variant of the Coproduct. /// /// # Example /// /// Composing with `subset` to match a subset of variants without /// consuming the coproduct: /// /// ``` /// # #[macro_use] extern crate frunk; fn main() { /// use frunk::Coproduct; /// /// let co: Coprod!(i32, bool, String) = Coproduct::inject(true); /// /// assert!(co.to_ref().subset::<Coprod!(&bool, &String), _>().is_ok()); /// # } /// ``` #[inline(always)] pub fn to_ref<'a>(&'a self) -> <Self as ToRef<'a>>::Output where Self: ToRef<'a>, { ToRef::to_ref(self) } /// Borrow each variant of the `Coproduct` mutably. /// /// # Example /// /// Composing with `subset` to match a subset of variants without /// consuming the coproduct: /// /// ``` /// # #[macro_use] extern crate frunk; fn main() { /// use frunk::Coproduct; /// /// let mut co: Coprod!(i32, bool, String) = Coproduct::inject(true); /// /// assert!(co.to_mut().subset::<Coprod!(&mut bool, &mut String), _>().is_ok()); /// # } /// ``` #[inline(always)] pub fn to_mut<'a>(&'a mut self) -> <Self as ToMut<'a>>::Output where Self: ToMut<'a>, { ToMut::to_mut(self) } /// Use functions to transform a Coproduct into a single value. /// /// A variety of types are supported for the `Folder` argument: /// /// * An `hlist![]` of closures (one for each type, in order). /// * A single closure (for a Coproduct that is homogenous). /// * A single [`Poly`]. /// /// [`Poly`]: ../traits/struct.Poly.html /// /// # Example /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// type I32F32StrBool = Coprod!(i32, f32, bool); /// /// let co1 = I32F32StrBool::inject(3); /// let co2 = I32F32StrBool::inject(true); /// let co3 = I32F32StrBool::inject(42f32); /// /// let folder = hlist![|&i| format!("int {}", i), /// |&f| format!("float {}", f), /// |&b| (if b { "t" } else { "f" }).to_string()]; /// /// assert_eq!(co1.to_ref().fold(folder), "int 3".to_string()); /// # } /// ``` /// /// Using a polymorphic function type has the advantage of not /// forcing you to care about the order in which you declare /// handlers for the types in your Coproduct. /// /// ``` /// # #[macro_use] extern crate frunk; /// # fn main() { /// use frunk::{Poly, Func}; /// /// type I32F32StrBool = Coprod!(i32, f32, bool); /// /// impl Func<i32> for P { /// type Output = bool; /// fn call(args: i32) -> Self::Output { /// args > 100 /// } /// } /// impl Func<bool> for P { /// type Output = bool; /// fn call(args: bool) -> Self::Output { /// args /// } /// } /// impl Func<f32> for P { /// type Output = bool; /// fn call(args: f32) -> Self::Output { /// args > 9000f32 /// } /// } /// struct P; /// /// let co1 = I32F32StrBool::inject(3); /// let folded = co1.fold(Poly(P)); /// # } /// ``` #[inline(always)] pub fn fold<Output, Folder>(self, folder: Folder) -> Output where Self: CoproductFoldable<Folder, Output>, { CoproductFoldable::fold(self, folder) } } /// Trait for instantiating a coproduct from an element /// /// This trait is part of the implementation of the inherent static method /// [`Coproduct::inject`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. In most code, `Coproduct::inject` will /// "just work," with or without this trait. /// /// [`Coproduct::inject`]: enum.Coproduct.html#method.inject pub trait CoprodInjector<InjectType, Index> { /// Instantiate a coproduct from an element. /// /// Please see the [inherent static method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent static method]: enum.Coproduct.html#method.inject fn inject(to_insert: InjectType) -> Self; } impl<I, Tail> CoprodInjector<I, Here> for Coproduct<I, Tail> { fn inject(to_insert: I) -> Self { Coproduct::Inl(to_insert) } } impl<Head, I, Tail, TailIndex> CoprodInjector<I, There<TailIndex>> for Coproduct<Head, Tail> where Tail: CoprodInjector<I, TailIndex>, { fn inject(to_insert: I) -> Self { let tail_inserted = <Tail as CoprodInjector<I, TailIndex>>::inject(to_insert); Coproduct::Inr(tail_inserted) } } // For turning something into a Coproduct --> /// Trait for borrowing a coproduct element by type /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::get`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. If you have a Coproduct of known type, /// then `co.get()` should "just work" even without the trait. /// /// [`Coproduct::get`]: enum.Coproduct.html#method.get pub trait CoproductSelector<S, I> { /// Borrow an element from a coproduct by type. /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.get fn get(&self) -> Option<&S>; } impl<Head, Tail> CoproductSelector<Head, Here> for Coproduct<Head, Tail> { fn get(&self) -> Option<&Head> { use self::Coproduct::*; match *self { Inl(ref thing) => Some(thing), _ => None, // Impossible } } } impl<Head, FromTail, Tail, TailIndex> CoproductSelector<FromTail, There<TailIndex>> for Coproduct<Head, Tail> where Tail: CoproductSelector<FromTail, TailIndex>, { fn get(&self) -> Option<&FromTail> { use self::Coproduct::*; match *self { Inr(ref rest) => rest.get(), _ => None, // Impossible } } } /// Trait for retrieving a coproduct element by type /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::take`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. If you have a Coproduct of known type, /// then `co.take()` should "just work" even without the trait. /// /// [`Coproduct::take`]: enum.Coproduct.html#method.take pub trait CoproductTaker<S, I> { /// Retrieve an element from a coproduct by type, ignoring all others. /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.take fn take(self) -> Option<S>; } impl<Head, Tail> CoproductTaker<Head, Here> for Coproduct<Head, Tail> { fn take(self) -> Option<Head> { use self::Coproduct::*; match self { Inl(thing) => Some(thing), _ => None, // Impossible } } } impl<Head, FromTail, Tail, TailIndex> CoproductTaker<FromTail, There<TailIndex>> for Coproduct<Head, Tail> where Tail: CoproductTaker<FromTail, TailIndex>, { fn take(self) -> Option<FromTail> { use self::Coproduct::*; match self { Inr(rest) => rest.take(), _ => None, // Impossible } } } /// Trait for folding a coproduct into a single value. /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::fold`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts or Folders of unknown type. If the type of everything is known, /// then `co.fold(folder)` should "just work" even without the trait. /// /// [`Coproduct::fold`]: enum.Coproduct.html#method.fold pub trait CoproductFoldable<Folder, Output> { /// Use functions to fold a coproduct into a single value. /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.fold fn fold(self, f: Folder) -> Output; } impl<P, R, CH, CTail> CoproductFoldable<Poly<P>, R> for Coproduct<CH, CTail> where P: Func<CH, Output = R>, CTail: CoproductFoldable<Poly<P>, R>, { fn fold(self, f: Poly<P>) -> R { use self::Coproduct::*; match self { Inl(r) => P::call(r), Inr(rest) => rest.fold(f), } } } impl<F, R, FTail, CH, CTail> CoproductFoldable<HCons<F, FTail>, R> for Coproduct<CH, CTail> where F: FnOnce(CH) -> R, CTail: CoproductFoldable<FTail, R>, { fn fold(self, f: HCons<F, FTail>) -> R { use self::Coproduct::*; let f_head = f.head; let f_tail = f.tail; match self { Inl(r) => (f_head)(r), Inr(rest) => rest.fold(f_tail), } } } /// This is literally impossible; CNil is not instantiable impl<F, R> CoproductFoldable<F, R> for CNil { fn fold(self, _: F) -> R { unreachable!() } } impl<'a, CH: 'a, CTail> ToRef<'a> for Coproduct<CH, CTail> where CTail: ToRef<'a>, { type Output = Coproduct<&'a CH, <CTail as ToRef<'a>>::Output>; #[inline(always)] fn to_ref(&'a self) -> Self::Output { match *self { Coproduct::Inl(ref r) => Coproduct::Inl(r), Coproduct::Inr(ref rest) => Coproduct::Inr(rest.to_ref()), } } } impl<'a> ToRef<'a> for CNil { type Output = CNil; fn to_ref(&'a self) -> CNil { match *self {} } } impl<'a, CH: 'a, CTail> ToMut<'a> for Coproduct<CH, CTail> where CTail: ToMut<'a>, { type Output = Coproduct<&'a mut CH, <CTail as ToMut<'a>>::Output>; #[inline(always)] fn to_mut(&'a mut self) -> Self::Output { match *self { Coproduct::Inl(ref mut r) => Coproduct::Inl(r), Coproduct::Inr(ref mut rest) => Coproduct::Inr(rest.to_mut()), } } } impl<'a> ToMut<'a> for CNil { type Output = CNil; fn to_mut(&'a mut self) -> CNil { match *self {} } } /// Trait for extracting a value from a coproduct in an exhaustive way. /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::uninject`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. If you have a Coproduct of known type, /// then `co.uninject()` should "just work" even without the trait. /// /// [`Coproduct::uninject`]: enum.Coproduct.html#method.uninject pub trait CoprodUninjector<T, Idx>: CoprodInjector<T, Idx> { type Remainder; /// Attempt to extract a value from a coproduct (or get the remaining possibilities). /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.uninject fn uninject(self) -> Result<T, Self::Remainder>; } impl<Hd, Tl> CoprodUninjector<Hd, Here> for Coproduct<Hd, Tl> { type Remainder = Tl; fn uninject(self) -> Result<Hd, Tl> { match self { Coproduct::Inl(h) => Ok(h), Coproduct::Inr(t) => Err(t), } } } impl<Hd, Tl, T, N> CoprodUninjector<T, There<N>> for Coproduct<Hd, Tl> where Tl: CoprodUninjector<T, N>, { type Remainder = Coproduct<Hd, Tl::Remainder>; fn uninject(self) -> Result<T, Self::Remainder> { match self { Coproduct::Inl(h) => Err(Coproduct::Inl(h)), Coproduct::Inr(t) => t.uninject().map_err(Coproduct::Inr), } } } /// Trait for extracting a subset of the possible types in a coproduct. /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::subset`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. If you have a Coproduct of known type, /// then `co.subset()` should "just work" even without the trait. /// /// [`Coproduct::subset`]: enum.Coproduct.html#method.subset pub trait CoproductSubsetter<Targets, Indices>: Sized { type Remainder; /// Extract a subset of the possible types in a coproduct (or get the remaining possibilities) /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.subset fn subset(self) -> Result<Targets, Self::Remainder>; } impl<Choices, THead, TTail, NHead, NTail, Rem> CoproductSubsetter<Coproduct<THead, TTail>, HCons<NHead, NTail>> for Choices where Self: CoprodUninjector<THead, NHead, Remainder = Rem>, Rem: CoproductSubsetter<TTail, NTail>, { type Remainder = <Rem as CoproductSubsetter<TTail, NTail>>::Remainder; /// Attempt to extract a value from a subset of the types. fn subset(self) -> Result<Coproduct<THead, TTail>, Self::Remainder> { match self.uninject() { Ok(good) => Ok(Coproduct::Inl(good)), Err(bads) => match bads.subset() { Ok(goods) => Ok(Coproduct::Inr(goods)), Err(bads) => Err(bads), }, } } } impl<Choices> CoproductSubsetter<CNil, HNil> for Choices { type Remainder = Self; #[inline(always)] fn subset(self) -> Result<CNil, Self::Remainder> { Err(self) } } /// Trait for converting a coproduct into another that can hold its variants. /// /// This trait is part of the implementation of the inherent method /// [`Coproduct::embed`]. Please see that method for more information. /// /// You only need to import this trait when working with generic /// Coproducts of unknown type. If you have a Coproduct of known type, /// then `co.embed()` should "just work" even without the trait. /// /// [`Coproduct::embed`]: enum.Coproduct.html#method.embed pub trait CoproductEmbedder<Out, Indices> { /// Convert a coproduct into another that can hold its variants. /// /// Please see the [inherent method] for more information. /// /// The only difference between that inherent method and this /// trait method is the location of the type parameters. /// (here, they are on the trait rather than the method) /// /// [inherent method]: enum.Coproduct.html#method.embed fn embed(self) -> Out; } impl CoproductEmbedder<CNil, HNil> for CNil { fn embed(self) -> CNil { match self { // impossible! } } } impl<Head, Tail> CoproductEmbedder<Coproduct<Head, Tail>, HNil> for CNil where CNil: CoproductEmbedder<Tail, HNil>, { fn embed(self) -> Coproduct<Head, Tail> { match self { // impossible! } } } impl<Head, Tail, Out, NHead, NTail> CoproductEmbedder<Out, HCons<NHead, NTail>> for Coproduct<Head, Tail> where Out: CoprodInjector<Head, NHead>, Tail: CoproductEmbedder<Out, NTail>, { fn embed(self) -> Out { match self { Coproduct::Inl(this) => Out::inject(this), Coproduct::Inr(those) => those.embed(), } } } #[cfg(test)] mod tests { use super::Coproduct::*; use super::*; #[test] fn test_coproduct_inject() { type I32StrBool = Coprod!(i32, &'static str, bool); let co1 = I32StrBool::inject(3); assert_eq!(co1, Inl(3)); let get_from_1a: Option<&i32> = co1.get(); let get_from_1b: Option<&bool> = co1.get(); assert_eq!(get_from_1a, Some(&3)); assert_eq!(get_from_1b, None); let co2 = I32StrBool::inject(false); assert_eq!(co2, Inr(Inr(Inl(false)))); let get_from_2a: Option<&i32> = co2.get(); let get_from_2b: Option<&bool> = co2.get(); assert_eq!(get_from_2a, None); assert_eq!(get_from_2b, Some(&false)); } #[test] #[cfg(feature = "std")] fn test_coproduct_fold_consuming() { type I32F32StrBool = Coprod!(i32, f32, bool); let co1 = I32F32StrBool::inject(3); let folded = co1.fold(hlist![ |i| format!("int {}", i), |f| format!("float {}", f), |b| (if b { "t" } else { "f" }).to_string(), ]); assert_eq!(folded, "int 3".to_string()); } #[test] fn test_coproduct_poly_fold_consuming() { type I32F32StrBool = Coprod!(i32, f32, bool); impl Func<i32> for P { type Output = bool; fn call(args: i32) -> Self::Output { args > 100 } } impl Func<bool> for P { type Output = bool; fn call(args: bool) -> Self::Output { args } } impl Func<f32> for P { type Output = bool; fn call(args: f32) -> Self::Output { args > 9000f32 } } struct P; let co1 = I32F32StrBool::inject(3); let folded = co1.fold(Poly(P)); assert_eq!(folded, false); } #[test] #[cfg(feature = "std")] fn test_coproduct_fold_non_consuming() { type I32F32Bool = Coprod!(i32, f32, bool); let co1 = I32F32Bool::inject(3); let co2 = I32F32Bool::inject(true); let co3 = I32F32Bool::inject(42f32); assert_eq!( co1.to_ref().fold(hlist![ |&i| format!("int {}", i), |&f| format!("float {}", f), |&b| (if b { "t" } else { "f" }).to_string(), ]), "int 3".to_string() ); assert_eq!( co2.to_ref().fold(hlist![ |&i| format!("int {}", i), |&f| format!("float {}", f), |&b| (if b { "t" } else { "f" }).to_string(), ]), "t".to_string() ); assert_eq!( co3.to_ref().fold(hlist![ |&i| format!("int {}", i), |&f| format!("float {}", f), |&b| (if b { "t" } else { "f" }).to_string(), ]), "float 42".to_string() ); } #[test] fn test_coproduct_uninject() { type I32StrBool = Coprod!(i32, &'static str, bool); let co1 = I32StrBool::inject(3); let co2 = I32StrBool::inject("hello"); let co3 = I32StrBool::inject(false); let uninject_i32_co1: Result<i32, _> = co1.uninject(); let uninject_str_co1: Result<&'static str, _> = co1.uninject(); let uninject_bool_co1: Result<bool, _> = co1.uninject(); assert_eq!(uninject_i32_co1, Ok(3)); assert!(uninject_str_co1.is_err()); assert!(uninject_bool_co1.is_err()); let uninject_i32_co2: Result<i32, _> = co2.uninject(); let uninject_str_co2: Result<&'static str, _> = co2.uninject(); let uninject_bool_co2: Result<bool, _> = co2.uninject(); assert!(uninject_i32_co2.is_err()); assert_eq!(uninject_str_co2, Ok("hello")); assert!(uninject_bool_co2.is_err()); let uninject_i32_co3: Result<i32, _> = co3.uninject(); let uninject_str_co3: Result<&'static str, _> = co3.uninject(); let uninject_bool_co3: Result<bool, _> = co3.uninject(); assert!(uninject_i32_co3.is_err()); assert!(uninject_str_co3.is_err()); assert_eq!(uninject_bool_co3, Ok(false)); } #[test] fn test_coproduct_subset() { type I32StrBool = Coprod!(i32, &'static str, bool); // CNil can be extracted from anything. let res: Result<CNil, _> = I32StrBool::inject(3).subset(); assert!(res.is_err()); if false { #[allow(unreachable_code)] { // ...including CNil. #[allow(unused)] let cnil: CNil = panic!(); let res: Result<CNil, _> = cnil.subset(); let _ = res; } } { // Order does not matter. let co = I32StrBool::inject(3); let res: Result<Coprod!(bool, i32), _> = co.subset(); assert_eq!(res, Ok(Coproduct::Inr(Coproduct::Inl(3)))); let co = I32StrBool::inject("4"); let res: Result<Coprod!(bool, i32), _> = co.subset(); assert_eq!(res, Err(Coproduct::Inl("4"))); } } #[test] fn test_coproduct_embed() { // CNil can be embedded into any coproduct. if false { #[allow(unreachable_code)] { #[allow(unused)] let cnil: CNil = panic!(); let _: CNil = cnil.embed(); #[allow(unused)] let cnil: CNil = panic!(); let _: Coprod!(i32, bool) = cnil.embed(); } } #[derive(Debug, PartialEq)] struct A; #[derive(Debug, PartialEq)] struct B; #[derive(Debug, PartialEq)] struct C; { // Order does not matter. let co_a = <Coprod!(C, A, B)>::inject(A); let co_b = <Coprod!(C, A, B)>::inject(B); let co_c = <Coprod!(C, A, B)>::inject(C); let out_a: Coprod!(A, B, C) = co_a.embed(); let out_b: Coprod!(A, B, C) = co_b.embed(); let out_c: Coprod!(A, B, C) = co_c.embed(); assert_eq!(out_a, Coproduct::Inl(A)); assert_eq!(out_b, Coproduct::Inr(Coproduct::Inl(B))); assert_eq!(out_c, Coproduct::Inr(Coproduct::Inr(Coproduct::Inl(C)))); } { // Multiple variants can resolve to the same output w/o type annotations type ABC = Coprod!(A, B, C); type BBB = Coprod!(B, B, B); let b1 = BBB::inject::<_, Here>(B); let b2 = BBB::inject::<_, There<Here>>(B); let out1: ABC = b1.embed(); let out2: ABC = b2.embed(); assert_eq!(out1, Coproduct::Inr(Coproduct::Inl(B))); assert_eq!(out2, Coproduct::Inr(Coproduct::Inl(B))); } } }