disjoint_base

This decorator marks a class as a disjoint base.

Child classes of a disjoint base cannot inherit from other disjoint bases that are
not parent or child classes of the disjoint base.

For example:

    @disjoint_base
    class Disjoint1: pass

    @disjoint_base
    class Disjoint2: pass

    class Disjoint3(Disjoint1, Disjoint2): pass  # Type checker error

Type checkers can use knowledge of disjoint bases to detect unreachable code
and determine when two types can overlap.