Some more details about the Ranges proposal that was well received by the ISO C++ committee at this month's meeting in Urbana-Champaign:

Container Algorithms

by Eric Niebler

From the article:

... So to sum up, in the world of N4128, we have this:

• Eager algorithms that can mutate but that don’t compose.
• Lazy algorithms that can’t mutate but do compose.

Whoops! Something is missing. If I want to read a bunch of ints, sort them, and make them unique, here’s what that would look like in N4128:

extern std::vector<int> read_ints();
std::vector<int> ints = read_ints();
std::sort(ints);
auto i = std::unique(ints);
ints.erase(i, ints.end());

Blech! A few people noticed this shortcoming of my proposal. A week before the meeting, I was seriously worried that this issue would derail the whole effort. I needed a solution, and quick.

Container Algorithms

The solution I presented in Urbana is container algorithms. These are composable algorithms that operate eagerly on container-like things, mutating them in-place, then forwarding them on for further processing. For instance, the read+sort+unique example looks like this with container algorithms:

std::vector<int> ints =
    read_ints() | cont::sort | cont::unique;

Much nicer. Since the container algorithm executes eagerly, it can take a vector and return a vector. The range views can’t do that...