These are all synonyms, even in type theory: > In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, di

These are all synonyms, even in type theory: > In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, disjoint union, sum type, or coproduct, is a data structure used to hold a value that could take on several different, but fixed, types. [1] C++ class inheritance is not a sum type for a couple reasons: - It does not allow you to discriminate on the type. - You can add RTTI, which allows you to discriminate, but then it is not a fixed set of types. Obviously, Rust does sum types better than C++, but that is really irrelevant. [1] https://en.wikipedia.org/wiki/Tagged_union https://en.wikipedia.org/wiki/Tagged_union