ptr_eq

[WIP] by-address comparisons and hashes in Rust.

Motivation

It is a common practice to identify an object by its address. Many programming languages with non-trivial runtime have native support for this pattern. For example, in Java and Python, two references are equal if they point to the same object. Even in system programming languages like C++, one may achieve this by using smart pointers like std::unique_ptr and std::shared_ptr, or just using raw pointers. The equality of these types is always determined by the pointer value.

This is, however, not the case in Rust. For example, in the default comparison implementation for &T compares the pointees, rather than the addresses. Smart pointers, like std::rc::Rc and std::sync::Arc, do so, as well. Only raw pointers, which are unsafe to use, compare by address. Typically, one should invoke special functions like std::ptr::eq to compare by address. This makes it inconvenient to determine the identity of two references by address.

This crate defines a trait PtrEq to indicate that references to this object compare equality by address. It also provides procedure macros to automatically derive these implementations, overriding the default Rust reference comparison rules.