tmp.rs

#![feature(specialization, never_type)]
use std::rc::Rc;
use std::sync::Arc;

pub trait Identity {
    type Type: ?Sized;
    fn identity(&self) -> *const ();
}

impl<T: ?Sized> Identity for T {
    default type Type = Self;
    default fn identity(&self) -> *const () {
        self as *const Self as *const ()
    }
}

impl<T: ?Sized> Identity for Box<T> {
    type Type = <T as Identity>::Type;

    fn identity(&self) -> *const () {
        (**self).identity()
    }
}

impl<'a, T: ?Sized> Identity for &'a T {
    type Type = <T as Identity>::Type;
    fn identity(&self) -> *const () {
        (**self).identity()
    }
}

impl<'a, T: ?Sized> Identity for &'a mut T {
    type Type = <T as Identity>::Type;

    fn identity(&self) -> *const () {
        (**self).identity()
    }
}

impl<T: ?Sized> Identity for Rc<T> {
    type Type = <T as Identity>::Type;

    fn identity(&self) -> *const () {
        (**self).identity()
    }
}

impl<T: ?Sized> Identity for Arc<T> {
    type Type = <T as Identity>::Type;
    fn identity(&self) -> *const () {
        (**self).identity()
    }
}

pub fn same<A: Identity, B: Identity<Type=A::Type>>(a: &A, b: &B) -> bool {
    a.identity() == b.identity()
}