Representing optional values with std::optional

Although quite a minor feature in C++17, std::optional is a neat addition to the STL library which simplifies a common case which couldn't be expressed in a clean straightforward syntax prior to std::optional. In a nutshell, it is a small wrapper for any type where the wrapped type can be both initialized and uninitialized.

To put it in C++ lingo, std::optional is a stack-allocated container with a max size of one.

Note that the Boost Libraries has had an equivalent of std::optional,named boost::optional for many years.

Optional return values

Before the introduction of std::optional, there was no clear way to define functions which may not return a defined value, such as...