[ves]

The typical way to do multiple instances for a given type is with trivial newtype wrappers for each instance. See the "Sum" and "Product" monoid instances (although these wrappers are also necessary for instance decidability). This is fine "in the wild."

Also, I'm not sure why you would ever want a "partial instance," as it would mean that your program could be unsafe but still typecheck (I haven't checked out Rust's implementation or motivation). Just use more specific classes, and you can even use a "generic" "instances of the components imply an instance of the whole" class and instance.

[jeremyjh]

When you specialize an instance in Rust, by definition it already has a valid instance that covers that type. So implementing a single method is fine - the other ones are provided by the instance you are specializing.

Newtypes also exist in Rust but this is an alternative that is not the same as the overlapping instances extension.