Is it possible to implement the equals operator for different types in Rust?

Question

As seen in How can an operator be overloaded for different RHS types and return values? you can implement some operators, eg. Add on multiple types using a work around.

Is a similar thing possible for the PartialEq trait?

I've tried various things, but the closest I can get is creating a fake trait Foo, implementing PartialEq on &Foo (since it's a trait you can't implement it on Foo) and then doing:

let x:Bar = ...
let y:FooBar = ...
if &x as &Foo == &y as &Foo {
  ...
}

The Equiv trait looks like it should be used for this, but as far as I can tell, implementing Equiv doesn't have anything to do with the == operator.

Is there a way to do this?

Answer 1

The == operator is only overridable via the PartialEq trait, and thus usable with matching types. Any other form of equality/equivalence needs a custom function/method, you can use the Equiv trait, although values that are equivalent should theoretically also have the same hash (or else HashMap.find_equiv won't work as you expect).