C++ - Ranges & Views Advanced

Overview

Estimated time: 70–90 minutes

Build expressive pipelines with C++20 ranges: filter, transform, take/drop, chunk, slide. Understand ownership, borrowed ranges, and when to materialize.

Learning Objectives

• Compose view pipelines and avoid dangling by materializing when needed.
• Use adaptors like views::filter, transform, take/drop, chunk, slide.
• Understand borrowed_range and range concepts in practice.

Prerequisites

• C++ - Algorithms & Ranges Deep Dive

View pipelines

#include 
#include 
#include 
int main(){
  std::vector v{1,2,3,4,5,6};
  auto pipe = v | std::views::filter([](int x){return x%2==0;})
                | std::views::transform([](int x){return x*x;})
                | std::views::take(2);
  for (int x: pipe) std::cout << x << ' '; // 4 16
}

Chunk and slide

#include 
#include 
#include 
int main(){
  std::vector v{1,2,3,4,5};
  for (auto chunk : v | std::views::chunk(2)){
    int sum = 0; for (int x : chunk) sum += x; std::cout << sum << ' '; // 3 7 5
  }
  std::cout << "\n";
  for (auto win : v | std::views::slide(3)){
    std::cout << win[0] << '+' << win[1] << '+' << win[2] << ' ';
  }
}

Borrowed ranges and dangling

#include 
#include 

std::ranges::take_view make_view(){
  std::vector tmp{1,2,3,4};
  return std::views::all(tmp) | std::views::take(2); // dangling! tmp dies
}

Fix: materialize into a container before returning, or return an owning view.

Common Pitfalls

• Returning non-owning views to temporary containers (dangling).
• Assuming pipelines materialize; views are lazy until copied to a container.

Checks for Understanding

1. When must you materialize a view?
2. What causes dangling in ranges?

Exercises

1. Use chunk and transform to compute moving sums; compare slide vs manual indexing.
2. Write a function that returns a materialized vector from a view pipeline to avoid dangling.