Sumty 🍵

sumty is a header-only C++20 library that provides "better" sum types. The C++ standard library provides std::variant, std::optional, and std::exepcted (as of C++23), but these have some limitiations that sumty aims to remove.

sumty provides four sum types, 3 of which correspond to one of the STL types mentioned above.

• variant - improved std::variant
• option - improved std::optional
• result - improved std::expected
• error_set - no STL equivalent but similar to std::variant

These sum types differ from those in the STL in a number of ways. Primarily, sumty's sum types extend alternatives to support references (lvalue and rvalue) and void. sumty also guarantees a few size optimizations that applies to all sum types, the boil down to taking advantage of empty types and the invariant that lvalue references are not null. Some size optimization examples are listed below.

• sizeof(variant<std::monostate, std::monostate>) == sizeof(bool)
• sizeof(option<int&>) == sizeof(void*)
• sizeof(result<void, void>) == sizeof(bool)
• sizeof(error_set<empty1, empty2, empty3>) == sizeof(uint8_t)