pub trait ConstMarker: Sized {
type Of;
const VAL: Self::Of;
}Expand description
A type that represents a constant
§Example
Emulating generic associated constants on stable
(this example Requires Rust 1.65.0)
ⓘ
use typewit::const_marker::{ConstMarker, ConstMarkerOf};
assert_eq!(make_array::<u8>(), ([3], [3, 3, 3]));
assert_eq!(make_array::<&str>(), (["hi"], ["hi", "hi", "hi"]));
const fn make_array<T: MakeArray>() -> ([T; 1], [T; 3]) {
(T::Make::<1>::VAL, T::Make::<3>::VAL)
}
// `MakeArray` can make arrays of any length without writing a bound for each length!!
trait MakeArray: Sized {
// emulates `const Make<const N: usize>: [Self; N];` (a generic associated constant)
type Make<const N: usize>: ConstMarkerOf<[Self; N]>;
}
impl MakeArray for u8 {
type Make<const N: usize> = MakeArrayConst<Self, N>;
}
impl<'a> MakeArray for &'a str {
type Make<const N: usize> = MakeArrayConst<Self, N>;
}
struct MakeArrayConst<T, const N: usize>(core::marker::PhantomData<T>);
impl<const N: usize> ConstMarker for MakeArrayConst<u8, N> {
type Of = [u8; N];
const VAL: Self::Of = [3; N];
}
impl<'a, const N: usize> ConstMarker for MakeArrayConst<&'a str, N> {
type Of = [&'a str; N];
const VAL: Self::Of = ["hi"; N];
}
Required Associated Constants§
Required Associated Types§
Dyn Compatibility§
This trait is not dyn compatible.
In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.