C++17 std::variant optimization guide as expected with custom types and visit function
Does anyone know how to I've been researching this but I've been banging my head against this for hours... I'm working with an scenario with `std::variant` in C++17 where the `std::visit` function doesn't seem to properly handle my custom types. I have defined a `std::variant` that can hold either a `std::string` or a custom struct `MyData`. When I try to use `std::visit`, I receive a compilation behavior related to the visitor function. Here’s the relevant part of my code: ```cpp #include <variant> #include <string> #include <iostream> struct MyData { int id; std::string name; }; int main() { std::variant<std::string, MyData> v; v = MyData{1, "Sample"}; auto visitor = [](auto&& arg) { std::cout << arg << '\n'; // Compilation behavior here }; std::visit(visitor, v); return 0; } ``` When I try to compile this, I get the behavior: `behavior: no matching function for call to 'std::visit(...)'`. I suspect the scenario lies in how I'm trying to output the `MyData` struct. I have not defined an `operator<<` for my struct, but I thought `std::visit` would handle it as long as it can access the member variables. I've tried adding an overload for `operator<<`, but I'm not sure how to best implement it. Here's what I attempted: ```cpp #include <ostream> std::ostream& operator<<(std::ostream& os, const MyData& data) { return os << "MyData{ id: " << data.id << ", name: " << data.name << " }"; } ``` However, integrating that with the `std::visit` is still causing issues. What’s the correct way to implement this so that `std::visit` can handle both `std::string` and `MyData` correctly? Any insights on making this work would be greatly appreciated! For context: I'm using C++ on Ubuntu. What's the best practice here? Could someone point me to the right documentation? The project is a mobile app built with C++. I'm open to any suggestions. This issue appeared after updating to C++ 3.11. Am I missing something obvious? This issue appeared after updating to C++ latest. I appreciate any insights!