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//! Marker types for passing constants as type arguments.
//!
//! # Example
//!
//! This example emulates specialization,
//! eliding a `.clone()` call when the created array is only one element long.
//!
//! ```rust
//! use typewit::{const_marker::Usize, TypeCmp, TypeEq};
//!
//! let arr = [3u8, 5, 8];
//!
//! assert_eq!(repeat(3), []);
//! assert_eq!(repeat(3), [3]);
//! assert_eq!(repeat(3), [3, 3]);
//! assert_eq!(repeat(3), [3, 3, 3]);
//! assert_eq!(repeat(3), [3, 3, 3, 3]);
//!
//!
//! fn repeat<T: Clone, const OUT: usize>(val: T) -> [T; OUT] {
//! // `te_len` ìs a `TypeEq<Usize<OUT>, Usize<1>>`
//! if let TypeCmp::Eq(te_len) = Usize::<OUT>.equals(Usize::<1>) {
//! // This branch is ran when `OUT == 1`
//! TypeEq::new::<T>() // returns `TypeEq<T, T>`
//! .in_array(te_len) // returns `TypeEq<[T; OUT], [T; 1]>`
//! .to_left([val]) // goes from `[T; 1]` to `[T; OUT]`
//! } else {
//! // This branch is ran when `OUT != 1`
//! [(); OUT].map(|_| val.clone())
//! }
//! }
//! ```
//!
//!
use crate::{
TypeEq,
TypeNe,
};
mod const_witnesses;
pub use const_witnesses::*;
#[cfg(feature = "adt_const_marker")]
mod slice_const_markers;
#[cfg(feature = "adt_const_marker")]
#[cfg_attr(feature = "docsrs", doc(cfg(feature = "adt_const_marker")))]
pub use slice_const_markers::Str;
/// Marker types for `const FOO: &'static [T]` parameters.
#[cfg(feature = "adt_const_marker")]
#[cfg_attr(feature = "docsrs", doc(cfg(feature = "adt_const_marker")))]
pub mod slice {
pub use super::slice_const_markers::{
BoolSlice,
CharSlice,
U8Slice,
U16Slice,
U32Slice,
U64Slice,
U128Slice,
UsizeSlice,
I8Slice,
I16Slice,
I32Slice,
I64Slice,
I128Slice,
IsizeSlice,
StrSlice,
};
}
struct Helper<L, R>(L, R);
macro_rules! __const_eq_with {
($L:ident, $R:ident) => {
$L == $R
};
($L:ident, $R:ident, ($L2:ident, $R2:ident) $cmp:expr) => ({
let $L2 = $L;
let $R2 = $R;
$cmp
});
} pub(crate) use __const_eq_with;
macro_rules! declare_const_param_type {
(
$(#[$struct_docs:meta])*
$struct:ident($prim:ty)
$(
$(#[$eq_docs:meta])*
fn equals $(($L:ident, $R:ident) $comparator:block)?;
)?
) => {
#[doc = concat!(
"Marker type for passing `const VAL: ", stringify!($prim),
"` as a type parameter."
)]
$(#[$struct_docs])*
#[derive(Debug, Copy, Clone)]
pub struct $struct<const VAL: $prim>;
impl<const L: $prim, const R: $prim> $crate::const_marker::Helper<$struct<L>, $struct<R>> {
const EQ: Result<
TypeEq<$struct<L>, $struct<R>>,
TypeNe<$struct<L>, $struct<R>>,
> = if crate::const_marker::__const_eq_with!(
L,
R
$($(, ($L, $R) $comparator)?)?
) {
// SAFETY: `L == R` (both are std types with sensible Eq impls)
// therefore `$struct<L> == $struct<R>`
unsafe {
Ok(TypeEq::<$struct<L>, $struct<R>>::new_unchecked())
}
} else {
// SAFETY: `L != R` (both are std types with sensible Eq impls)
// therefore `$struct<L> != $struct<R>`
unsafe {
Err(TypeNe::<$struct<L>, $struct<R>>::new_unchecked())
}
};
const EQUALS: crate::TypeCmp<$struct<L>, $struct<R>> = match Self::EQ {
Ok(x) => crate::TypeCmp::Eq(x),
Err(x) => crate::TypeCmp::Ne(x),
};
}
impl<const VAL: $prim> $struct<VAL> {
/// Compares `self` and `other` for equality.
///
/// Returns:
/// - `Ok(TypeEq)`: if `VAL == OTHER`
/// - `Err(TypeNe)`: if `VAL != OTHER`
///
#[inline(always)]
#[deprecated(note = "superceeded by `equals` method", since = "1.8.0")]
pub const fn eq<const OTHER: $prim>(
self,
_other: $struct<OTHER>,
) -> Result<
TypeEq<$struct<VAL>, $struct<OTHER>>,
TypeNe<$struct<VAL>, $struct<OTHER>>,
> {
$crate::const_marker::Helper::<$struct<VAL>, $struct<OTHER>>::EQ
}
/// Compares `self` and `other` for equality.
///
/// Returns:
/// - `TypeCmp::Eq(TypeEq)`: if `VAL == OTHER`
/// - `TypeCmp::Ne(TypeNe)`: if `VAL != OTHER`
///
$($(#[$eq_docs])*)?
#[inline(always)]
pub const fn equals<const OTHER: $prim>(
self,
_other: $struct<OTHER>,
) -> crate::TypeCmp<$struct<VAL>, $struct<OTHER>> {
$crate::const_marker::Helper::<$struct<VAL>, $struct<OTHER>>::EQUALS
}
}
};
} pub(crate) use declare_const_param_type;
declare_const_param_type!{
Bool(bool)
///
/// For getting a type witness that
/// `Bool<B>` is either `Bool<true>` or `Bool<false>`,
/// you can use [`BoolWit`].
///
fn equals;
}
declare_const_param_type!{Char(char)}
declare_const_param_type!{U8(u8)}
declare_const_param_type!{U16(u16)}
declare_const_param_type!{U32(u32)}
declare_const_param_type!{U64(u64)}
declare_const_param_type!{U128(u128)}
declare_const_param_type!{
Usize(usize)
/// # Examples
///
/// ### Array
///
/// This example demonstrates how `Usize` can be used to
/// specialize behavior on array length.
///
/// (this example requires Rust 1.61.0, because it uses trait bounds in const fns)
#[cfg_attr(not(feature = "rust_1_61"), doc = "```ignore")]
#[cfg_attr(feature = "rust_1_61", doc = "```rust")]
/// use typewit::{const_marker::Usize, TypeCmp, TypeEq};
///
/// assert_eq!(try_from_pair::<_, 0>((3, 5)), Ok([]));
/// assert_eq!(try_from_pair::<_, 1>((3, 5)), Ok([3]));
/// assert_eq!(try_from_pair::<_, 2>((3, 5)), Ok([3, 5]));
/// assert_eq!(try_from_pair::<_, 3>((3, 5)), Err((3, 5)));
///
///
/// const fn try_from_pair<T: Copy, const LEN: usize>(pair: (T, T)) -> Result<[T; LEN], (T, T)> {
/// if let TypeCmp::Eq(te_len) = Usize::<LEN>.equals(Usize::<0>) {
/// // this branch is ran on `LEN == 0`
/// // `te_len` is a `TypeEq<Usize<LEN>, Usize<0>>`
/// Ok(
/// TypeEq::new::<T>() // `TypeEq<T, T>`
/// .in_array(te_len) // `TypeEq<[T; LEN], [T; 0]>`
/// .to_left([]) // Goes from `[T; 0]` to `[T; LEN]`
/// )
/// } else if let TypeCmp::Eq(te_len) = Usize.equals(Usize) {
/// // this branch is ran on `LEN == 1`
/// // `te_len` is inferred to be `TypeEq<Usize<LEN>, Usize<1>>`
/// Ok(TypeEq::NEW.in_array(te_len).to_left([pair.0]))
/// } else if let TypeCmp::Eq(te_len) = Usize.equals(Usize) {
/// // this branch is ran on `LEN == 2`
/// // `te_len` is inferred to be `TypeEq<Usize<LEN>, Usize<2>>`
/// Ok(TypeEq::NEW.in_array(te_len).to_left([pair.0, pair.1]))
/// } else {
/// Err(pair)
/// }
/// }
///
/// ```
///
/// ### Struct
///
/// This example demonstrates how `Usize` can be used to pass a
/// const-generic struct to a function expecting a concrete type of that struct.
///
/// ```rust
/// use typewit::{const_marker::Usize, TypeCmp};
///
/// assert_eq!(mutate(Array([])), Array([]));
/// assert_eq!(mutate(Array([3])), Array([3]));
/// assert_eq!(mutate(Array([3, 5])), Array([3, 5]));
/// assert_eq!(mutate(Array([3, 5, 8])), Array([8, 5, 3])); // reversed!
/// assert_eq!(mutate(Array([3, 5, 8, 13])), Array([3, 5, 8, 13]));
///
///
/// #[derive(Debug, PartialEq)]
/// struct Array<const CAP: usize>([u32; CAP]);
///
/// const fn mutate<const LEN: usize>(arr: Array<LEN>) -> Array<LEN> {
/// match Usize::<LEN>.equals(Usize::<3>) {
/// // `te_len` is a `TypeEq<Usize<LEN>, Usize<3>>`
/// // this branch is ran on `LEN == 3`
/// TypeCmp::Eq(te_len) => {
/// // `te` is a `TypeEq<Array<LEN>, Array<3>>`
/// let te = te_len.project::<GArray>();
///
/// // `te.to_right(...)` here goes from `Array<LEN>` to `Array<3>`
/// let ret = reverse3(te.to_right(arr));
///
/// // `te.to_left(...)` here goes from `Array<3>` to `Array<LEN>`
/// te.to_left(ret)
/// }
/// TypeCmp::Ne(_) => arr,
/// }
/// }
///
/// const fn reverse3(Array([a, b, c]): Array<3>) -> Array<3> {
/// Array([c, b, a])
/// }
///
/// typewit::type_fn!{
/// // Type-level function from `Usize<LEN>` to `Array<LEN>`
/// struct GArray;
///
/// impl<const LEN: usize> Usize<LEN> => Array<LEN>
/// }
/// ```
fn equals;
}
declare_const_param_type!{I8(i8)}
declare_const_param_type!{I16(i16)}
declare_const_param_type!{I32(i32)}
declare_const_param_type!{I64(i64)}
declare_const_param_type!{I128(i128)}
declare_const_param_type!{Isize(isize)}