Auto function returning value using switch

Question

I'm trying to create a function which return type should depend on switch statement, something like:

auto function_name (int value) {
    switch (value) {
        case 1 : {return 2.3;}
        case 2 : {return 1;}
        case 3 : {return "string";}
    }
}

But I can't because of an error:

error: inconsistent deduction for auto return type: 'double' and then 'int'

What can I do to create something similar by functionality to the example above?

Answer 1

A function in C++ can only have a single type that it returns. If you use auto as the return type and you have different return statements that return different types then the code is ill-formed as it violates the single type rule.

This where std::variant or std::any needs to be used. If you have a few different types that could be returned via some run-time value then you could use either of those types as "generic type". std::variant is more restrictive as you have to specify the types it could be, but it also less expensive then std::any because you know what types it could be.

std::variant<double, int, std::string> function_name (int value) {
    using namespace std::literals::string_literals;
    switch (value) {
        case 1 : {return 2.3;}
        case 2 : {return 1;}
        case 3 : {return "string"s;} // use ""s here to force it to be a std::string
    }
}

Will let you return different types.