Sorting algorithms are a fundamental topic in computer science, and they play a crucial role in various applications. In this blog post, we will explore the concept of coroutine-based sorting algorithms and how they can be implemented in C++. By utilizing coroutines, we can achieve efficient and readable sorting code that takes advantage of cooperative multitasking.

Introducing Coroutines

Coroutines are a powerful feature introduced in C++20 that allows functions to be suspended and resumed later. This feature enables a new paradigm of programming known as coroutine-based programming. By leveraging coroutines, we can write asynchronous code that is more readable, maintainable, and efficient.

Coroutine-Based Sorting Algorithm

One of the most widely used sorting algorithms is the QuickSort algorithm. Let’s demonstrate how we can implement a coroutine-based QuickSort algorithm in C++.

#include <iostream>
#include <vector>
#include <coroutine>

using namespace std;

template<typename T>
struct sorter {
    vector<T>& data;
    
    struct promise_type {
        sorter get_return_object() {
            return {coroutine_handle<promise_type>::from_promise(*this), data};
        }
        
        suspend_never initial_suspend() { return {}; }
        
        suspend_never final_suspend() noexcept { return {}; }
        
        void unhandled_exception() {}
        
        void return_void() {}
        
        auto yield_value(T value) {
            data.push_back(value);
            return suspend_always{};
        }
    };
    
    bool operator co_await() {
        return !data.empty();
    }
    
    coroutine_handle<promise_type> coro;
    
    sorter(coroutine_handle<promise_type> coro, vector<T>& data)
    : coro(coro), data(data) {}
    
    ~sorter() {
        if(coro)
            coro.destroy();
    }
};

template<typename T>
auto operator co_await(sorter<T>& s) {
    return std::exchange(s.coro, {});;
}

template<typename T>
sorter<T> operator|(vector<T>& data, sorter<T> s) {
    return s;
}

template<typename T>
sorter<T> quicksort(vector<T>& data) {
    if(data.size() <= 1)
        co_return;
        
    T pivot = data.front();
    vector<T> lower;
    vector<T> equal;
    vector<T> greater;
    
    for(auto&& value : data) {
        co_await ((value < pivot) ? lower : (value > pivot) ? greater : equal) | [&] { return value; };
    }
    
    co_await quicksort(lower);
    co_await quicksort(greater);
    
    move(begin(lower), end(lower), begin(data));
    move(begin(equal), end(equal), begin(data) + lower.size());
    move(begin(greater), end(greater), end(data) - greater.size());
}

int main() {
    vector<int> data = {5, 3, 2, 1, 4};
    
    cout << "Before Sorting: ";
    for(auto&& value : data)
        cout << value << " ";
    cout << endl;
    
    data | quicksort<int>;
    
    cout << "After Sorting: ";
    for(auto&& value : data)
        cout << value << " ";
    cout << endl;
    
    return 0;
}

In the above code, we define a sorter struct that represents a coroutine. The get_return_object function returns a sorter instance, which serves as the coroutine handle. We implement the yield_value function to add elements to the data vector, and the operator co_await checks if the data vector is not empty.

The quicksort function is a coroutine-based implementation of the QuickSort algorithm. It utilizes recursive coroutines to sort the lower and greater partitions. We use the co_await operator to suspend the execution until the recursive quicksort calls are completed.

In the main function, we demonstrate the usage of the coroutine-based quicksort function by sorting a vector of integers. We pipe the data vector into the quicksort function using the | operator.

Conclusion

In this blog post, we explored the concept of coroutine-based sorting algorithms in C++. We leveraged the power of coroutines to implement a coroutine-based QuickSort algorithm. By using coroutines, we can write efficient and readable code that takes advantage of cooperative multitasking. Coroutine-based sorting algorithms open up new possibilities for writing high-performance sorting code in C++. So, next time you need to implement a sorting algorithm, consider using coroutines to make your code more elegant and efficient!

#tech #C++ #sorting #coroutines