The use of boost::hana::for_each function and sample code

The use of boost::hana::for_each function and sample code

boost::hana is a C++ metaprogramming library that provides tools such as containers, algorithms, and operators commonly used in metaprogramming. Among them, the for_each function is a function to traverse the container, and can perform the specified operation on each element in the container. This article will introduce one of the overloaded versions of for_each_fn and demonstrate its usage through sample code.

First, you need to reference the boost/hana/for_each.hpp header file in the code, and then you can use the for_each function. The function prototype of for_each_fn is as follows:

template
constexpr auto for_each_fn(F&& f);

where F is a function object type that accepts one parameter representing each element in the container.

The following is a sample code that demonstrates how to use the for_each_fn function to count the number of odd and even numbers in an array of integers:

#include <iostream>
#include <boost/hana.hpp>

int main() {
    int arr[] = {1, 2, 3, 4, 5};
    int even_cnt = 0, odd_cnt = 0;
    boost::hana::for_each_fn([&even_cnt, &odd_cnt](auto x) {
        if (x % 2 == 0) {
            even_cnt++;
        } else {
            odd_cnt++;
        }
    })(boost::hana::make_range(arr, arr + sizeof(arr)/sizeof(int)));

    std::cout <&l