Advanced Ranges and Views

Why ranges matter

Ranges let you express data flow directly: filter, transform, slice, then consume. This often reads closer to the problem than manual iterator code.

auto ids = users
    | std::views::filter([](const User& user) { return user.active; })
    | std::views::transform([](const User& user) { return user.id; });

Lazy vs materialized results

The pipeline above is lazy. It does not create a new container automatically.

That is useful when:

• the source range is still alive
• you only need one pass
• you want to avoid unnecessary allocation

Materialize into a container when you need stable ownership or repeated traversal.

Projections simplify algorithms

std::ranges::sort(users, std::greater<>{}, &User::score);

This sorts by score without writing a custom comparator body.

A complete example

std::vector<std::string> top_names(const std::vector<User>& users) {
    auto view = users
        | std::views::filter([](const User& user) { return user.score >= 90; })
        | std::views::transform([](const User& user) { return user.name; });

    return {view.begin(), view.end()};
}

Common pitfalls

• Returning a view to data that will not outlive the view.
• Packing too much logic into one unreadable pipeline.
• Forgetting that lazy views may recompute work on each iteration.

Exercises

• Replace a loop-based filter-and-transform sequence with a view pipeline.
• Sort a vector of structs using a projection.
• Decide where in one existing function the pipeline should become a concrete container.