重新定义类成员数据类型

Question

Is it possible to change the data type of a class member after its initialization? Say, redefine a double named "Foo" to a string?

Answer 1

No. Types are fixed at compile time. If you want to switch between double and a string perhaps reach for a std::variant :

std::variant<double, std::string> val = 1.0;
val = std::string("hello");

Answer 2

As answer to your comment, you should use std::optional

std::optional<int> Do(int x, int y)
{   
    if ( x == y ) 
    {
        return 42; 
    }

    return {}; 
}   

int main()
{   
    auto ret = Do(3,2); // << exchange your test data here!
    if ( ret ) 
    {   
        std::cout << "Got an answer" << ret.value() << std::endl;
    }   
    else
    {   
        std::cout << "No answer" << std::endl;
    }
}