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//! This module holds the machinery behind LabelledGeneric. //! //! A LabelledGeneric instance is pretty much exactly the same as a Generic instance, except //! that the generic representation should contain information about field names. //! //! Having a separate trait for LabelledGenerics gives us the freedom to derive both //! lablled and non-labelled generic type class instances for our types. //! //! Asides from the main LabelledGeneric trait, this module holds helper methods that allow //! users to use LabelledGeneric without using universal function call syntax. //! //! In addition, this module holds macro-generated enums that map to letters in field names (identifiers). use std::marker::PhantomData; use hlist::*; /// A trait that converts from a type to a labelled generic representation /// /// For the most part, you should be using the derivation that is available through /// frunk_derive to generate instances of this typeclass for your types. /// /// I would highly recommend you check out `derivation_tests.rs` to see how to actually use /// this trait in real life. Since frunk_derive depends on this trait, I can't actually /// pull it in as a dependency here (otherwise the dependency would be circular) and show /// how to use it in a proper doc test. /// /// ```rust,ignore /// #[derive(LabelledGeneric)] /// struct NewUser<'a> { /// first_name: &'a str, /// last_name: &'a str, /// age: usize, /// } /// /// #[derive(LabelledGeneric)] /// struct SavedUser<'a> { /// first_name: &'a str, /// last_name: &'a str, /// age: usize, /// } /// /// let n_user = NewUser { /// first_name: "Joe", /// last_name: "Blow", /// age: 30, /// }; /// /// let s_user = <SavedUser as LabelledGeneric>::convert_from(n_user); // done /// ``` pub trait LabelledGeneric { /// The labelled generic representation type type Repr; /// Go from something to Repr fn into(self) -> Self::Repr; /// Go from labelled Repr to something fn from(r: Self::Repr) -> Self; /// From one type to another using a type with a compatible labelled generic representation fn convert_from<A>(a: A) -> Self where A: LabelledGeneric<Repr = Self::Repr>, Self: Sized { let repr = <A as LabelledGeneric>::into(a); <Self as LabelledGeneric>::from(repr) } /// Converts from another type A into Self assuming that A and Self have labelled generic representations /// that can be sculpted into each other. /// /// Note that this method tosses away the "remainder" of the sculpted representation. In other /// words, anything that is not needed from A gets tossed out. fn sculpted_convert_from<A, Indices>(a: A) -> Self where A: LabelledGeneric, Self: Sized, // The labelled representation of A must be sculpt-able into the labelled representation of Self <A as LabelledGeneric>::Repr: Sculptor<<Self as LabelledGeneric>::Repr, Indices> { let a_gen = <A as LabelledGeneric>::into(a); // We toss away the remainder. let (self_gen, _): (<Self as LabelledGeneric>::Repr, _) = a_gen.sculpt(); <Self as LabelledGeneric>::from(self_gen) } } /// Given a labelled generic Representation of an A, returns A pub fn from_labelled_generic<A, Repr>(gen: Repr) -> A where A: LabelledGeneric<Repr = Repr> { <A as LabelledGeneric>::from(gen) } /// Given an A, returns its labelled generic Representation pub fn into_labelled_generic<A, Repr>(a: A) -> Repr where A: LabelledGeneric<Repr = Repr> { <A as LabelledGeneric>::into(a) } /// Converts one type into another assuming they have the same labelled generic Representation pub fn labelled_convert_from<A, B, Repr>(a: A) -> B where A: LabelledGeneric<Repr = Repr>, B: LabelledGeneric<Repr = Repr> { <B as LabelledGeneric>::convert_from(a) } /// Converts from one type into another assuming that their labelled generic representations /// can be sculpted into each other. /// /// The "Indices" type parameter allows the compiler to figure out that the two representations /// can indeed be morphed into each other. pub fn sculpted_convert_from<A, B, Indices>(a: A) -> B where A: LabelledGeneric, B: LabelledGeneric, // The labelled representation of A must be sculpt-able into the labelled representation of B <A as LabelledGeneric>::Repr: Sculptor<<B as LabelledGeneric>::Repr, Indices> { <B as LabelledGeneric>::sculpted_convert_from(a) } // Create a bunch of enums that can be used to represent characters on the type level macro_rules! create_enums_for { ($($i: ident)*) => { $( #[allow(non_snake_case, non_camel_case_types)] #[derive(PartialEq, Debug, Eq, Clone, Copy, PartialOrd, Ord)] pub enum $i {} )* } } // Add more as needed. create_enums_for! { a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z __ _1 _2 _3 _4 _5 _6 _7 _8 _9 _0 } #[derive(PartialEq, Debug, Eq, Clone, Copy, PartialOrd, Ord)] pub struct Labelled<Name, Type> { name: PhantomData<Name>, pub value: Type, } /// Helper function for building a new Labelled value. /// /// Useful so that users don't need to deal with PhantomData directly. /// /// ``` /// # use frunk_core::labelled::*; /// let f1 = label::<(a, g, e), i32>(3); /// let f2 = label::<(a, g, e), i32>(3); /// assert_eq!(f1, f2) /// /// ``` pub fn label<Label, Value>(value: Value) -> Labelled<Label, Value> { Labelled { name: PhantomData, value: value, } } /// Trait for turning a Labelled HList into an un-labelled HList pub trait IntoUnlabelled { type Output; /// Turns the current HList into an unlabelled on. /// /// Effectively extracts the values held inside the individual Labelled /// /// ``` /// # #[macro_use] extern crate frunk_core; /// # use frunk_core::labelled::*; /// # use frunk_core::hlist::*; /// # fn main() { /// /// let labelled_hlist = hlist![ /// label::<(n, a, m, e), &str>("joe"), /// label::<(a, g, e), i32>(3) /// ]; /// /// let unlabelled = labelled_hlist.into_unlabelled(); /// /// assert_eq!(unlabelled, hlist!["joe", 3]) /// # } /// ``` fn into_unlabelled(self) -> Self::Output; } /// Implementation for HNil impl IntoUnlabelled for HNil { type Output = HNil; fn into_unlabelled(self) -> Self::Output { self } } /// Implementation when we have a non-empty HCons holding a label in its head impl<Label, Value, Tail> IntoUnlabelled for HCons<Labelled<Label, Value>, Tail> where Tail: IntoUnlabelled { type Output = HCons<Value, <Tail as IntoUnlabelled>::Output>; fn into_unlabelled(self) -> Self::Output { HCons { head: self.head.value, tail: self.tail.into_unlabelled(), } } } #[cfg(test)] mod tests { use super::*; #[test] fn test_field_construction() { let f1 = label::<(a, g, e), i32>(3); let f2 = label::<(a, g, e), i32>(3); assert_eq!(f1, f2) } #[test] fn test_unlabelling() { let labelled_hlist = hlist![ label::<(n, a, m, e), &str>("joe"), label::<(a, g, e), i32>(3)]; let unlabelled = labelled_hlist.into_unlabelled(); assert_eq!(unlabelled, hlist!["joe", 3]) } }