derive_more/
as.rs

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1//! Type glue for [autoref-based specialization][0], used in [`AsRef`]/[`AsMut`] macro expansion.
2//!
3//! Allows tp specialize the `impl<T> AsRef<T> for T` case over the default
4//! `impl<Inner: AsRef<B>, B> AsRef<B> for Outer<Inner>` one.
5//!
6//! [0]: https://lukaskalbertodt.github.io/2019/12/05/generalized-autoref-based-specialization.html
7
8use core::marker::PhantomData;
9
10/// Container to specialize over.
11pub struct Conv<Frm: ?Sized, To: ?Sized>(PhantomData<(*const Frm, *const To)>);
12
13impl<Frm: ?Sized, To: ?Sized> Default for Conv<Frm, To> {
14    fn default() -> Self {
15        Self(PhantomData)
16    }
17}
18
19/// Trait performing the specialization.
20pub trait ExtractRef {
21    /// Input reference type.
22    type Frm;
23    /// Output reference type.
24    type To;
25
26    /// Extracts the output type from the input one.
27    fn __extract_ref(&self, frm: Self::Frm) -> Self::To;
28}
29
30impl<'a, T> ExtractRef for &Conv<&'a T, T>
31where
32    T: ?Sized,
33{
34    type Frm = &'a T;
35    type To = &'a T;
36
37    fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
38        frm
39    }
40}
41
42impl<'a, Frm, To> ExtractRef for Conv<&'a Frm, To>
43where
44    Frm: AsRef<To> + ?Sized,
45    To: ?Sized + 'a,
46{
47    type Frm = &'a Frm;
48    type To = &'a To;
49
50    fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
51        frm.as_ref()
52    }
53}
54
55impl<'a, T> ExtractRef for &Conv<&'a mut T, T>
56where
57    T: ?Sized,
58{
59    type Frm = &'a mut T;
60    type To = &'a mut T;
61
62    fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
63        frm
64    }
65}
66
67impl<'a, Frm, To> ExtractRef for Conv<&'a mut Frm, To>
68where
69    Frm: AsMut<To> + ?Sized,
70    To: ?Sized + 'a,
71{
72    type Frm = &'a mut Frm;
73    type To = &'a mut To;
74
75    fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
76        frm.as_mut()
77    }
78}
derive_more/as.rs

derive_more/
as.rs
