4 ms·
Inheritance (the subtyping part of it) is considered the OOP way to write sum type. sum Expr { Int; Add(Int,Int) } VS class Expr { } class Add extends
by maattdd 2y ago
Inheritance (the subtyping part of it) is considered the OOP way to write sum type.
sum Expr {
Int;
Add(Int,Int)
}
VS
class Expr {
}
class Add extends Expr {
Expr left;
Expr right;
}
- searealist 2y agoThat's not C++.
- maattdd 2y agoAny reader who comment here hopefully has enough knowledge to understand the implied C++. struct Add {} std::variant<Add, int> Expr; OR class Expr {} class Add : Expr {}
- searealist 2y agoI dont think you have ever seriously used c++.
- deleted 2y ago[deleted]
- gpderetta 2y agoThe expression problem enters the room.
- OvbiousError 2y agoYou should probably look up what a sum type is, it has nothing to do with summations. Your example doesn't contain a sum type. A C++ example: std:variant<int,std::string> sum_type_instance = 5;
- maattdd 2y agoMy sum type example is exactly this (but I didn't use C++ std::variant<> syntax to not confuse the reader). The most common example of a sum type is the "Expression problem" - please read some literature before commenting on a topic. (Btw, it's called sum type for a reason: summation. The cardinality of the sum type is the sum of the cardinality of its variants)
- Maxatar 2y agoYou seem to have a very narrow C++ view of what sum types are. Sum types are related to the expression problem, and the given example is the canonical instance of the expression problem. https://en.wikipedia.org/wiki/Expression_problem https://en.wikipedia.org/wiki/Expression_problem
- searealist 2y agoSum types are not “anything that can encode an expression”. They have a precise definition. They are closed and a synonym for a tagged union.
- Maxatar 2y agoPlease use quotes to refer to a statement that someone has actually made. Doing otherwise is an indicator that you are making a strawman argument.
- searealist 2y agoToday you learned what a sum type is. Just admit your ignorance and move on with your life. Maybe bookmark this: https://en.wikipedia.org/wiki/Tagged_union https://en.wikipedia.org/wiki/Tagged_union
- Maxatar 2y agoLooks like you are very easily triggered on this topic. Quite amusing to be honest :)
- tialaramex 2y ago"synonym for a tagged union" Tagged unions are an implementation and one that's often a poor fit for the problem. Sum types are an idea from type theory, rather than an implementation detail. It's very on-brand for C++ to have standardized a poor implementation detail rather than the useful idea. Look at how much hoop jumping was required to make std::optional<T&> work for C++ 26 and then compare how Rust's Option<&T> isn't even special, that's just naturally what happens.