C++ STL reduce 用法

一：功能

累加求和，它是 std::accumulate 的泛化版本，它元素的累加顺序没有要求，因此可以用于并行累加。另外也可以通过重载运算符进行累乘等运算。

二：用法

#include <iostream>
#include <vector>
#include <numeric>
#include <execution>

int main() {
    std::vector<int> data{1, 2, 3, 4, 5};

    auto sum = std::reduce(data.begin(), data.end(), 0);
    std::cout << "sum == " << sum << "\n";

    sum = std::reduce(std::execution::par_unseq,
        data.begin(), data.end(), 0);
    std::cout << "sum (parallel) == " << sum << "\n";

    auto product = std::reduce(data.begin(), data.end(), 1,
        std::multiplies<>{});
    std::cout << "product == " << product << "\n";

    product = std::reduce(std::execution::par_unseq,
        data.begin(), data.end(), 1, std::multiplies<>{});
    std::cout << "product (parallel) == " << product << "\n";        
}

#include <iostream>
#include <vector>
#include <numeric>
#include <execution>

//通过重载 + 运算符，实现自定义类型的累加操作
struct Foo {
	std::string sound = "Foo";
	Foo operator+(const Foo& right) const {
		return {sound+right.sound};
	}
};

int main() {
    std::vector<Foo> data(2, Foo{});
    Foo final_Foo = std::reduce(data.begin(), data.end());
    
    std::cout << "final_Foo.sound == " << final_Foo.sound << "\n";
    //final_Foo.sound == FooFooFoo
}