pub type CallInjFn<F, A> = <F as InjTypeFn<A>>::Ret;
Expand description
CallFn
with an additional F:
InjTypeFn<A>
requirement,
which helps with type inference.
§Example
use typewit::{InjTypeFn, CallInjFn};
// inferred return type
let inferred_ret = upcast(3u8);
assert_eq!(inferred_ret, 3);
// inferred argument type
let inferred_arg: u32 = upcast(5);
assert_eq!(inferred_arg, 5);
// Because the return type is `CallInjFn<_, I>`,
// this can infer `I` from the return type,
fn upcast<I>(int: I) -> CallInjFn<Upcast, I>
where
Upcast: InjTypeFn<I>,
CallInjFn<Upcast, I>: From<I>,
{
int.into()
}
typewit::inj_type_fn!{
struct Upcast;
impl u8 => u16;
impl u16 => u32;
impl u32 => u64;
impl u64 => u128;
}
As of October 2023, replacing CallInjFn
with CallFn
can cause type inference errors:
error[E0277]: the trait bound `Upcast: TypeFn<{integer}>` is not satisfied
--> src/type_fn/injective.rs:132:32
|
11 | let inferred_arg: u32 = upcast(5);
| ------ ^ the trait `TypeFn<{integer}>` is not implemented for `Upcast`
| |
| required by a bound introduced by this call
|
= help: the following other types implement trait `TypeFn<T>`:
<Upcast as TypeFn<u16>>
<Upcast as TypeFn<u32>>
<Upcast as TypeFn<u64>>
<Upcast as TypeFn<u8>>