Hello there! Today, we'll explore an exciting feature in C++ called the pipe operator and how it works with the Boost.Range library. Have you ever wondered how you can easily chain operations together in a clear and concise way? That's exactly what we'll learn!

By the end of this lesson, you'll know how to use the pipe operator to filter and transform ranges in C++. Sounds fun, right? Let's get started!

Imagine you're making a sandwich. First, you take bread, then you add cheese, and finally, you add lettuce. The pipe operator in C++ works similarly. It lets you chain one operation into the next, like adding ingredients step-by-step.

In C++, the | operator is used with Boost.Range to connect different operations like filtering and transforming. This makes your code neat and easy to read. By using the pipe operator, you can apply multiple transformations to a range in a sequential manner without cluttering your code with nested function calls.

Let's break down a simple example to understand how the pipe operator works with Boost.Range.

First, let's set up our code. We'll include Boost adaptors and write a simple program that filters out even numbers from a list and then squares them. Here's the setup:

C++
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1#include <boost/range/adaptor/transformed.hpp>
2#include <boost/range/adaptor/filtered.hpp>
3#include <iostream>
4#include <vector>
5
6bool is_even(int x) {
7    return x % 2 == 0;
8}
9
10int square(int x) {
11    return x * x;
12}
13
14int main() {
15    std::vector<int> nums = {1, 2, 3, 4, 5, 6, 7, 8, 9};
16    return 0; // Placeholder for pipe operations
17}

We'll start by filtering even numbers from our list. The filter operation checks each number and keeps only those that are even.

C++
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1auto result = nums | boost::adaptors::filtered(is_even);

The boost::adaptors::filtered function takes a predicate that checks if a number is even. We have already seen the pipe operator in such example, now let's talk more about how it works:

• Left-hand Side: The left-hand side of the | operator is usually the range you want to operate on. For example, nums in our example.
• Right-hand Side: The right-hand side of the | operator is the operation you want to apply to the range. This operation can be a filter, a transformation, or any other range adaptor provided by Boost.

When chained together, the operations are applied from left to right, making the data flow through each operation in sequence.

Let's add square to the chain using the pipe operator:

C++
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1auto result = nums 
2              | boost::adaptors::filtered(is_even)
3              | boost::adaptors::transformed(square);

The boost::adaptors::transformed function applies the square function to each element of the result of the boost::adaptors::filtered.

Here's the complete code with both filtering and transformation:

C++
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1#include <boost/range/adaptor/transformed.hpp>
2#include <boost/range/adaptor/filtered.hpp>
3#include <boost/range/algorithm/for_each.hpp>
4#include <iostream>
5#include <vector>
6
7bool is_even(int x) {
8    return x % 2 == 0;
9}
10
11int square(int x) {
12    return x * x;
13}
14
15int main() {
16    std::vector<int> nums = {1, 2, 3, 4, 5, 6, 7, 8, 9};
17
18    auto result = nums
19                  | boost::adaptors::filtered(is_even)
20                  | boost::adaptors::transformed(square);
21
22    boost::for_each(result, [](int n) {
23        std::cout << n << " ";  // Output: 4 16 36 64 
24    });
25
26    return 0;
27}

When you run this code, it will output the squared values of all even numbers in the list.

Our code filtered out the odd numbers and then squared the even ones, all in a clear way thanks to the pipe operator!

Great job! Today, we learned about the pipe operator and how it makes our code clean and concise. We explored filtering and transforming ranges using Boost.Range by chaining operations.

Now that we've covered the theory and examples, it's time for some hands-on practice. You'll try these concepts yourself and see how powerful and convenient the pipe operator is. Let's move on to some practice exercises to deepen your understanding!