The std::any type is similar in one regard to std::optional--it has a has_value() method that tells if an instance carries a value or not. But apart from that, it can contain literally anything, so it is more complex to handle compared with optional.

Before accessing the content of an any variable, we need to find out what type it carries and, then, cast it to that type.

Finding out if an any instance holds a type T value can be done with a comparison: x.type() == typeid(T). If this comparison results in true, then we can use any_cast to get at the content.

Note that any_cast<T>(x) returns a copy of the internal T value in x. If we want a reference in order to avoid copying of complex objects, we need to use any_cast<T&>(x). This is what we did when we accessed the internal string or list<int> objects in this section's code.