Create views into containers with ranges

The new ranges library is one of the more significant additions to C++20. It provides a new paradigm for filtering and processing containers. Ranges provide clean and intuitive building blocks for more effective and readable code.

Let's start by defining a few terms:

• A Range is a collection of objects which can be iterated. In other words, any structure that supports the begin() and end() iterators is a range. This includes most STL containers.
• A View is a range that transforms another underlying range. Views are lazy, meaning they only operate as the range iterates. A view returns data from the underlying range and does not own any data itself. Views operate in O(1) constant time.
• A View Adapter is an object that takes a range and returns a view object. A view adapter may be chained with other view adapters using the | operator.

  Note

  The <ranges> library uses the std::ranges and the std::ranges::view namespaces....