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//! Type glue for [autoref-based specialization][0], used in [`AsRef`]/[`AsMut`] macro expansion.
//!
//! Allows tp specialize the `impl<T> AsRef<T> for T` case over the default
//! `impl<Inner: AsRef<B>, B> AsRef<B> for Outer<Inner>` one.
//!
use core::marker::PhantomData;
/// Container to specialize over.
pub struct Conv<Frm: ?Sized, To: ?Sized>(PhantomData<(*const Frm, *const To)>);
impl<Frm: ?Sized, To: ?Sized> Default for Conv<Frm, To> {
fn default() -> Self {
Self(PhantomData)
}
}
/// Trait performing the specialization.
pub trait ExtractRef {
/// Input reference type.
type Frm;
/// Output reference type.
type To;
/// Extracts the output type from the input one.
fn __extract_ref(&self, frm: Self::Frm) -> Self::To;
}
impl<'a, T> ExtractRef for &Conv<&'a T, T>
where
T: ?Sized,
{
type Frm = &'a T;
type To = &'a T;
fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
frm
}
}
impl<'a, Frm, To> ExtractRef for Conv<&'a Frm, To>
where
Frm: AsRef<To> + ?Sized,
To: ?Sized + 'a,
{
type Frm = &'a Frm;
type To = &'a To;
fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
frm.as_ref()
}
}
impl<'a, T> ExtractRef for &Conv<&'a mut T, T>
where
T: ?Sized,
{
type Frm = &'a mut T;
type To = &'a mut T;
fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
frm
}
}
impl<'a, Frm, To> ExtractRef for Conv<&'a mut Frm, To>
where
Frm: AsMut<To> + ?Sized,
To: ?Sized + 'a,
{
type Frm = &'a mut Frm;
type To = &'a mut To;
fn __extract_ref(&self, frm: Self::Frm) -> Self::To {
frm.as_mut()
}
}