On: Why should I have written ZeroMQ in C, not C++ (2012)

[Koshkin]

That requires 1 bit of information, and there is often a way of embedding that bit in the value itself; but the general technique of representing alternatives is called “a tagged union.” (You can also hear the fancy terms “the product type” for the struct and “the sum type” for the union.)

[lixtra → Koshkin]

Accessing that one bit can be as expensive as passing an int around.