[vram22]

Most familiar with Python currently. Done some Ruby and Java and C and Pascal earlier. Some D and a bit of C++ and a bit of Go. I do understand that structs and tuples are examples of product types (because the range of the values for a struct or tuple is the Cartesian product of all the possible values for each field). My question was mainly about sum types as described by rbehrends, was trying to relate them in my mind (somewhat, if it makes sense) to traditional inheritance as in Python, Java or C++.

[Sean1708]

Cool, so unions in C and C++ are a kind of sum type because the variable can have one of a set of types. More usually people think of tagged unions when they think of sum types, I believe Pascal's Variant Records are an example of tagged unions.

[vram22]

Thanks. Yes, I was thinking on the same lines. Don't remember whether Pascal also has this right now (more time since I used it than C), but in C, being the somewhat more flexible language that it is, IIRC you can also store a value of one type (out of the types of the sum type) in the union, and then read it back out as one of the other types. E.g. define a union with an int (say 16-bit) and a two-char (or two-byte) array, and then write into it as an int, and read it back out as two chars or two bytes. There are uses for such things, though I can't think of a good example of the top of my head. Okay, one use might be hardware interfacing, another might be conversion between big-endian and little-endian data values if you need to roll your own for some reason, I know there are libs for that).