hooman

// The correct implementation of `Equatable` (and `Comparable`) can be tricky for class
// hierarchies. To make it easier, it is better to follow a well-defined pattern. Here
// is my suggestion on how to do it:

// 1. Define a protocol for polymorphic test function for equality (or comparison): 
// Note: operators are not polymorphic (not virtual in C++ terms)). The function to 
// call is determined and hard-coded at compile time.

/// A protocol to ammend `Equatable` for use with `class` types.