More C++20 features

C++20 is a new big release of the C++ language. It contains many features that make the language more complex and flexible. Concepts, ranges, and coroutines are some of the many features that will be discussed throughout the book.

One of the most anticipated features is modules, which provide the ability to declare modules and export types and values within those modules. You can consider modules an improved version of header files with the now redundant include-guards. We'll cover C++20 modules in this chapter.

Besides notable features added in C++20, there is a list of other features that we will discuss throughout the book:

• The spaceship operator: operator<=>(). The verbosity of operator overloading can now be controlled by leveraging operator<=>().
• constexpr conquers more and more space in the language. C++20 now has the consteval function, constexpr std::vector and std::string, and many more.
• Math constants, such as std::number::pi and std::number::log2e.
• Major updates to the Thread library, including stop tokens and joining threads.
• The iterator concepts.
• Move-only views and other features.

To better understand some new features and also dive into the essence of the language, we will introduce the language's core starting from previous versions. This will help us to find better uses for new features compared to older ones, and will also help in supporting legacy C++ code. Let's now start by gaining an understanding of the C++ application building-process.