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. Recognizing that this is cumbersome, the standard includes an alias for std::ranges::view as the simply, std::view. This is still fairly cumbersome. For this recipe we will use the following aliases, to save space and because it is somewhat more elegant:

• namespace ranges = std::ranges; // save the fingers!

• namespace views = std::ranges::views;

This applies to all the code in this recipe.

How to do it

The ranges and views classes are in the <ranges> header. Let's look at how we can use them:

• A view is applied to a range, like this: