Ranges Views: Lazy, Non-Mutating Iterations with Materialization

Views are non-owning ranges with complexity guarantees

Any type that provides the functions begin() and end(), where begin() returns an iterator and end() returns a sentinel, qualifies as a range. We concluded that all standard containers are ranges. Containers own their elements, so we can, therefore, call them owning ranges.

A view is also a range, that is, it provides begin() and end() functions. However, unlike containers, a view does not own the elements in the range that the view spans over.

The construction of a view is required to be a constant-time operation, $O(1)$. It cannot perform any work that depends on the size of the underlying container. The same goes for assigning, copying, moving, and destructing a view. This makes it easy to reason about performance when using views to combine multiple algorithms. ...