Creating reference of box

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16

Also, the section

  • TyCtor(T) to TyCtor(U), where TyCtor(T) is one of

    • &T
    • &mut T
    • *const T
    • *mut T
    • Box<T>

    and where U can be obtained from T by unsized coercion.

Is kinda weird, because it seems to merely try to list the CoerceUnsize in the standard library while being awefully incomplete. I.e. this section appears to be a natural language description of this list of impls

impl<'a, 'b, T, U> CoerceUnsized<&'a U> for &'b T
where
    'b: 'a,
    T: Unsize<U> + ?Sized,
    U: ?Sized,

impl<'a, T, U> CoerceUnsized<&'a mut U> for &'a mut T
where
    T: Unsize<U> + ?Sized,
    U: ?Sized,

impl<T, U> CoerceUnsized<*const U> for *const T
where
    T: Unsize<U> + ?Sized,
    U: ?Sized,

impl<T, U> CoerceUnsized<*mut U> for *mut T
where
    T: Unsize<U> + ?Sized,
    U: ?Sized

impl<T, U, A> CoerceUnsized<Box<U, A>> for Box<T, A>
where
    T: Unsize<U> + ?Sized,
    A: Allocator,
    U: ?Sized,

while the standard library has a lot more CoerceUnsized impls.

Now I’m wondering why the impls for &T and &mut T are different w.r.t. the lifetimes. An oversight?