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//! Marker trait for types that implement the const formatting methods. //! //! use crate::polymorphism::CmpWrapper; use core::marker::PhantomData; //////////////////////////////////////////////////////////////////////////////// /// Marker trait for types that implement the const comparison methods. /// pub trait ConstCmpMarker { /// What kind of type this is, this can be one of: /// /// - [`IsArrayKind`]: For slices, and arrays. /// /// - [`IsStdKind`]: Any other standard library type. /// /// - [`IsNotStdKind`]: Any type that is not from the standard library. /// /// [`IsArrayKind`]: ./struct.IsArrayKind.html /// [`IsStdKind`]: ./struct.IsStdKind.html /// [`IsNotStdKind`]: ./struct.IsNotStdKind.html type Kind; /// The type after dereferencing, /// implemented as `type This = Self;` for all non-reference types type This: ?Sized; } /// Marker type for arrays and slices, /// used as the [`Kind`] associated type in [`ConstCmpMarker`]. /// /// [`Kind`]: ./trait.ConstCmpMarker.html#associatedtype.Kind /// [`ConstCmpMarker`]: ./trait.ConstCmpMarker.html /// pub struct IsArrayKind<T>(PhantomData<T>); /// Marker type for the remaining standard library types,, /// used as the [`Kind`] associated type in [`ConstCmpMarker`]. /// /// [`Kind`]: ./trait.ConstCmpMarker.html#associatedtype.Kind /// [`ConstCmpMarker`]: ./trait.ConstCmpMarker.html /// pub struct IsStdKind; /// Marker type for non-standard library types, /// used as the [`Kind`] associated type in [`ConstCmpMarker`]. /// /// [`Kind`]: ./trait.ConstCmpMarker.html#associatedtype.Kind /// [`ConstCmpMarker`]: ./trait.ConstCmpMarker.html /// pub struct IsNotStdKind; /////////////////////////////////////////////////////////////////////////////// /// Hack used to automatically wrap standard library types inside [`CmpWrapper`], /// while leaving user defined types unwrapped. /// /// # Type parameters /// /// `K` is `<R as ConstCmpMarker>::Kind` /// The kind of type that `T` is, /// [a slice](./struct.IsArrayKind.html), /// [other std types](./struct.IsStdKind.html), /// [non-std types](./struct.IsNotStdKind.html). /// /// `T` is `<R as ConstCmpMarker>::This`, /// the `R` type after removing all layers of references. /// /// # Coerce Method /// /// The `coerce` method is what does the conversion from a `&T` depending on /// the `K` type parameter: /// /// - [`IsArrayKind`]: the reference is coerced to a slice, and wrapped in a [`CmpWrapper`]. /// /// - [`IsStdKind`]: the referenced value is copied, and wrapped in a [`CmpWrapper`]. /// /// - [`IsNotStdKind`]: the reference is simply returned as a `&T`. /// /// [`IsArrayKind`]: ./struct.IsArrayKind.html /// [`IsStdKind`]: ./struct.IsStdKind.html /// [`IsNotStdKind`]: ./struct.IsNotStdKind.html /// /// [`CmpWrapper`]: ../struct.CmpWrapper.html /// #[allow(clippy::type_complexity)] pub struct IsAConstCmpMarker<K, T: ?Sized, R: ?Sized>( PhantomData<( PhantomData<fn() -> PhantomData<K>>, PhantomData<fn() -> PhantomData<T>>, PhantomData<fn() -> PhantomData<R>>, )>, ); impl<K, T: ?Sized, R: ?Sized> Copy for IsAConstCmpMarker<K, T, R> {} impl<K, T: ?Sized, R: ?Sized> Clone for IsAConstCmpMarker<K, T, R> { fn clone(&self) -> Self { *self } } impl<R> IsAConstCmpMarker<R::Kind, R::This, R> where R: ?Sized + ConstCmpMarker, { /// Constructs an `IsAConstCmpMarker` pub const NEW: Self = Self(PhantomData); } impl<K, T: ?Sized, R: ?Sized> IsAConstCmpMarker<K, T, R> { /// Infers the type parameters by taking a reference to `R` . /// /// The `K` and `T` type parameters are determined by `R` in /// the [`NEW`] associated constant. /// /// [`NEW`]: #associatedconstant.NEW #[inline(always)] pub const fn infer_type(self, _: &R) -> Self { self } /// Removes layers of references by coercing the argument. #[inline(always)] pub const fn unreference(self, r: &T) -> &T { r } } ///////////////////////////////////////////////////////////////////////////// impl<U, T: ?Sized, R: ?Sized> IsAConstCmpMarker<IsArrayKind<U>, T, R> { /// Coerces an array to a slice, then wraps the slice in a `CmpWrapper` #[inline(always)] pub const fn coerce(self, slice: &[U]) -> CmpWrapper<&[U]> { CmpWrapper(slice) } } impl<T: ?Sized, R: ?Sized> IsAConstCmpMarker<IsNotStdKind, T, R> { /// An identity function, just takes `reference` and returns it. #[inline(always)] pub const fn coerce(self, reference: &T) -> &T { reference } } ///////////////////////////////////////////////////////////////////////////// #[cfg(feature = "const_generics")] macro_rules! array_impls { ($($tt:tt)*) => { impl<T, const N: usize> ConstCmpMarker for [T; N] { type Kind = IsArrayKind<T>; type This = Self; } }; } #[cfg(not(feature = "const_generics"))] macro_rules! array_impls { ($($len:literal),* $(,)* ) => ( $( impl<T> ConstCmpMarker for [T; $len] { type Kind = IsArrayKind<T>; type This = Self; } )* ) } impl ConstCmpMarker for str { type Kind = IsStdKind; type This = Self; } impl<R: ?Sized> IsAConstCmpMarker<IsStdKind, str, R> { /// Wraps `reference` in a `CmpWrapper`. #[inline(always)] pub const fn coerce(self, reference: &str) -> CmpWrapper<&str> { CmpWrapper(reference) } } array_impls! { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15, 16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31, 32, } impl<T> ConstCmpMarker for [T] { type Kind = IsArrayKind<T>; type This = [T]; } impl<T> ConstCmpMarker for &T where T: ?Sized + ConstCmpMarker, { type Kind = T::Kind; type This = T::This; } impl<T> ConstCmpMarker for &mut T where T: ?Sized + ConstCmpMarker, { type Kind = T::Kind; type This = T::This; }