std::optional with std::variant: How to Return an Optional Variant from a Function in C++20?
I'm upgrading from an older version and I'm stuck trying to I'm maintaining legacy code that I'm experimenting with After trying multiple solutions online, I still can't figure this out..... I'm working on a personal project and I'm working on a C++20 project where I need to return a `std::optional<std::variant<int, std::string>>` from a function. My goal is to return either an integer, a string, or nothing if the operation fails. I've defined my function like this: ```cpp #include <optional> #include <variant> #include <string> #include <iostream> std::optional<std::variant<int, std::string>> fetchData(bool shouldFail) { if (shouldFail) { return std::nullopt; // Failure case } else { return 42; // Success case, returning an int } } ``` However, when I try to use the returned value like this: ```cpp int main() { auto result = fetchData(false); if (result) { // Attempting to access the value std::visit([](auto&& arg) { std::cout << arg << '\n'; }, *result); } else { std::cout << "No data available!" << '\n'; } } ``` I get a compilation behavior: ``` behavior: no matching function for call to ‘std::variant<int, std::string>::visit(...)’ ``` I suspect this has to do with how I'm trying to use `std::visit` with the `std::optional` but I'm not sure how to fix it. I've tried changing the way I access the value using `std::get_if` instead, but that also leads to complications when handling the variant. Is there a more appropriate way to structure this code, or am I missing something in the usage of `std::visit` with `std::optional`? Any insights would be greatly appreciated! My development environment is macOS. Is there a better approach? Hoping someone can shed some light on this. Thanks, I really appreciate it! I'm working in a CentOS environment. The stack includes C++ and several other technologies.