Trait typewit::type_fn::RevTypeFn

pub trait RevTypeFn<Ret: ?Sized>: TypeFn<Self::Arg, Output = Ret> {
    type Arg: ?Sized;
}

The inverse of TypeFn, for getting the argument of a TypeFn from its return value.

Properties

These are properties about RevTypeFn that users can rely on.

For any given F: RevTypeFn<R> + RevTypeFn<O> these hold:

1. If R == O, then UncallFn<F, R> == UncallFn<F, O>

2. If R != O, then UncallFn<F, R> != UncallFn<F, O>

Disclaimer: this trait does not by itself ensure that a function is injective, since RevTypeFn<Ret> can’t know if Self::Arg is the only argument that could produce Ret.

Examples

Macro-based impl

use std::ops::Range;

use typewit::{RevTypeFn, UncallFn};

let array = [3usize, 5];

// Getting the argument of `ArrayFn` from its return value
let value: UncallFn<ArrayFn<2>, [usize; 2]> = array[0];

assert_eq!(value, 3usize);

typewit::inj_type_fn!{
    struct ArrayFn<const N: usize>;
    impl<T> T => [T; N]
}

Manual impl

use std::ops::Range;

use typewit::{CallInjFn, RevTypeFn, TypeFn, UncallFn};

let array = [3usize, 5];

// Getting the argument of `ArrayFn` from its return value
let value: UncallFn<ArrayFn<2>, [usize; 2]> = array[0];

assert_eq!(value, 3usize);

struct ArrayFn<const N: usize>;

impl<T, const N: usize> TypeFn<T> for ArrayFn<N> {
    type Output = [T; N];

    // Ensures that this impl of `TypeFn` for `ArrayFn` is injective.
    const TYPE_FN_ASSERTS: () = { let _: CallInjFn<Self, T>; };
}
impl<T, const N: usize> RevTypeFn<[T; N]> for ArrayFn<N> {
    type Arg = T;
}

Non-injective function

As mentioned above, this trait doesn’t make a function injective.

In the example below, NonInjective isn’t injective, because it maps different arguments to the same return value:

use typewit::{CallFn, RevTypeFn, TypeFn, UncallFn};
 
let _: CallFn<NonInjective, Vec<u8>> = 3u8;
let _: CallFn<NonInjective, String> = 5u8;
 
let _: UncallFn<NonInjective, u8> = ();
 
 
struct NonInjective;
 
impl<T> TypeFn<T> for NonInjective {
    type Output = u8;
}
 
impl RevTypeFn<u8> for NonInjective {
    type Arg = ();
}

Required Associated Types

type Arg: ?Sized

The argument to this function with Ret as the return value.

Object Safety

This trait is not object safe.

Implementations on Foreign Types

impl<F, R: ?Sized> RevTypeFn<R> for PhantomData<F>

where F: RevTypeFn<R>,

type Arg = <F as RevTypeFn<R>>::Arg

Implementors

impl<'a, T: 'a + ?Sized> RevTypeFn<&'a T> for GRef<'a>

type Arg = T

impl<'a, T: 'a + ?Sized> RevTypeFn<&'a mut T> for GRefMut<'a>

type Arg = T

impl<F, R: ?Sized> RevTypeFn<R> for FnRev<F>

where F: InjTypeFn<R>,

type Arg = <F as InjTypeFn<R>>::Ret

impl<F, R: ?Sized> RevTypeFn<R> for Invoke<F>

where F: RevTypeFn<R>,

type Arg = <F as RevTypeFn<R>>::Arg

impl<T: ?Sized> RevTypeFn<Box<T>> for GBox

type Arg = T

impl<T: ?Sized> RevTypeFn<T> for FnIdentity

type Arg = T