Wrap up

Things to remember

Here are the things to remember about std::variant:

• It holds one of several alternatives in a type-safe way

• No extra memory allocation is needed. The variant needs the size of the max of the sizes of the alternatives, plus some little extra space for knowing the currently active value

• By default, it initialises with the default value of the first alternative

• You can access the value through std::get, std::get_if or through a form of a visitor

• To check the currently active type you can use std::holds_alternative or std::variant::index

• std::visit provides a way to perform an operation that is implemented for any possible type that might currently be the active one in the variant. Such a polymorphic operation is represented by a callable object that implements its call-operator for every possible type that this variant can hold

• Rarely std::variant might get into an invalid state, you can check this issue with the valueless_by_exception() method