Modern C++ Programming Cookbook

How to do it...

To visit a variant, you must provide one or more actions for the possible alternatives of the variant. There are several types of visitors that are used for different purposes:

• A void visitor that does not return anything, but has side-effects. The following example prints the title of each DVD to the console:

        for (auto const & d : dvds)        {          std::visit([](auto&& arg) {                        std::cout << arg.title << std::endl; },                      d);        }

• A visitor that returns a value; the value should have the same type regardless of the current alternative of the variant, or can be itself a variant. In the following example, we visit a variant and return a new variant of the same type that has the title property from any of its alternatives transformed to uppercase ...