C++17 STL Cookbook

How it works...

Working with optional is generally very simple and convenient. If we want to attach the notion of possible failure or optionality to any type T, we can just wrap it into std::optional<T> and that's it.

Whenever we get such a value from somewhere, we have to check whether it is in the empty state or whether it contains a real value. The bool optional::has_value() function does that for us. If it returns true, we may access the value. Accessing the value of an optional can be done with T& optional::value().

Instead of always writing if (x.has_value()) {...} and x.value(), we can also write if (x) {...} and *x. The std::optional type defines explicit conversion to bool and operator* in such a way that dealing with an optional ...