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/*! Framework for partial function handling (where some functionality is implemented for some but not all of the data types of fields in a data structure). A specific piece of partially-implemented functionality consists of a [Func](trait.Func.html) implementation for all data types where the functionality exists, a [FuncDefault](trait.FuncDefault.html) implementation for data types where the functionality doesn't exist, and [IsImplemented](trait.IsImplemented.html) specification for all data types denoting whether to use the available `Func` or the fall-back `FuncDefault`. This module should be unnecessary once [trait specialization](https://github.com/rust-lang/rust/issues/31844) is finalized. */ use std::marker::PhantomData; use access::DataIndex; use cons::*; use fieldlist::*; use label::{LVCons, SelfValued, TypedValue, Valued}; use view::{AssocDataIndexConsOf, DataIndexCons}; /// Marker struct denoting that a [Func](trait.Func.html) is implemented for a particular data type. #[derive(Debug, Clone)] pub struct Implemented; /// Marker struct denoting that a [Func](trait.Func.html) is not implemented for a particular data /// type. #[derive(Debug, Clone)] pub struct Unimplemented; /// Marker struct for combination of a data type, [Func](trait.Func.html), and whether or not that /// combination has an implementation. #[derive(Debug, Clone)] pub struct Capabilities<DType, Fun, IsImpl> { _marker: PhantomData<(DType, Fun, IsImpl)>, } /// Structure tracking a field (as accessed through a type that implements /// [DataIndex](../access/trait.DataIndex.html)) along with its /// [Capabilities](struct.Capabilities.html) details. #[derive(Debug, Clone)] pub struct StorageCapabilities<DType, DI, Fun, IsImpl> where DI: DataIndex<DType = DType>, { _marker: PhantomData<Capabilities<DType, Fun, IsImpl>>, data: DI, } impl<'a, DType, DI, Fun, IsImpl> SelfValued for StorageCapabilities<DType, DI, Fun, IsImpl> where DI: DataIndex<DType = DType> { } /// A cons-list of [StorageCapabilities](struct.StorageCapabilities.html) structs. pub type StorageCapabilitiesCons<Label, DType, DI, Fun, IsImpl, Tail> = LVCons<Label, StorageCapabilities<DType, DI, Fun, IsImpl>, Tail>; /// Trait denoting whether a particular [Func](trait.Func.html) is implemented for a data type. pub trait IsImplemented<Fun> { /// Marker trait (either [Implemented](struct.Implemented.html) or /// [Unimplemented](struct.Unimplemented.html)) specifying the implementation status for this /// function / data type combination. type IsImpl; } /// Trait for applying a partially-implemented function [Func](trait.Func.html) to a cons-list. pub trait PartialMap<F> { /// The output of the function, constructed into a cons-list of function results. type Output; /// Apply the function `F` to the value in this element of a cons-list, and recurse. fn map(&self, f: &mut F) -> Self::Output; } impl<'a, F> PartialMap<F> for Nil { type Output = Nil; fn map(&self, _f: &mut F) -> Nil { Nil } } impl<'a, Label, DType, DI, Fun, Tail, F> PartialMap<F> for StorageCapabilitiesCons<Label, DType, DI, Fun, Implemented, Tail> where Tail: PartialMap<F>, F: Func<DType>, DI: DataIndex<DType = DType>, { type Output = FieldPayloadCons<Label, DType, F::Output, Tail::Output>; fn map(&self, f: &mut F) -> Self::Output { FieldPayloadCons { head: TypedValue::from(f.call(&self.head.value_ref().data)).into(), tail: self.tail.map(f), } } } impl<'a, Label, DType, DI, Fun, Tail, F> PartialMap<F> for StorageCapabilitiesCons<Label, DType, DI, Fun, Unimplemented, Tail> where Tail: PartialMap<F>, DI: DataIndex<DType = DType>, F: FuncDefault, { type Output = FieldPayloadCons<Label, DType, F::Output, Tail::Output>; fn map(&self, f: &mut F) -> Self::Output { FieldPayloadCons { head: TypedValue::from(f.call()).into(), tail: self.tail.map(f), } } } /// Implementation of a function for a particular data type. pub trait Func<DType> { /// Output of this function. type Output; /// Method to call this function on field data of data type `DType`. fn call<DI>(&mut self, data: &DI) -> Self::Output where DI: DataIndex<DType = DType>; } /// Default function implementation with no valid implementation exists. pub trait FuncDefault { /// Output of this function. type Output; /// Method called when no [Func](trait.Func.html) implementation exists. fn call(&mut self) -> Self::Output; } /// Trait that augments a [DataIndexCons](../view/type.DataIndexCons.html) (a cons-list of /// field access structs) with partial-function capability information as specified by /// [IsImplemented](trait.IsImplemented.html) definitions. pub trait DeriveCapabilities<F> { /// The augmented cons-list which implements [PartialMap](trait.PartialMap.html), allowing /// application of partially-implemented functions to a `DataView`. type Output: PartialMap<F>; /// Derive the capabilities of this cons-list. fn derive(self) -> Self::Output; } impl<F> DeriveCapabilities<F> for Nil { type Output = Nil; fn derive(self) -> Nil { Nil } } impl<Label, DType, DI, Tail, F> DeriveCapabilities<F> for DataIndexCons<Label, DType, DI, Tail> where Tail: DeriveCapabilities<F>, DI: DataIndex<DType = DType> + SelfValued, DType: IsImplemented<F>, StorageCapabilitiesCons< Label, DType, DI, F, <DType as IsImplemented<F>>::IsImpl, <Tail as DeriveCapabilities<F>>::Output, >: PartialMap<F>, { type Output = StorageCapabilitiesCons< Label, DType, DI, F, <DType as IsImplemented<F>>::IsImpl, <Tail as DeriveCapabilities<F>>::Output, >; fn derive(self) -> Self::Output { LVCons { head: StorageCapabilities { data: self.head.value(), _marker: PhantomData, } .into(), tail: self.tail.derive(), } } } /// Helper type alias that provides the derived capabilities of the /// [DataIndexCons](../view/type.DataIndexCons.html) associated with a particular `Labels` / /// `Frames` pair. pub type DeriveCapabilitiesOf<Labels, Frames, F> = <AssocDataIndexConsOf<Labels, Frames> as DeriveCapabilities<F>>::Output;