[REQUEST] Allow operator overloading of user defined wp.struct types

[mmacklin]

Description

It would be useful to be able to overload operators, i.e.: add(), sub(), mul(), for user defined @WP.struct types.

This could be accomplished by having users define @wp.func overloads for add(), mul() that accept the user type.

Context

An example where this is useful would be e.g.: complex numbers or interval arithmetic which could be implemented completely within Python using this approach.