[c++] Higher order functions examples

hof.cpp

#include <iostream>
#include <cstdio>
#include <map>
#include <vector>
#include <algorithm>

namespace {
    std::vector<int> vec = {1, 2, 3};
    void result(bool ret, const char *func) {
            printf("%s result: ", func);
        if (ret)
            printf("true\n");
        else
            printf("false\n");
    }

    void transform() {
        std::vector<int> out;
        std::transform(vec.begin(), vec.end(), std::back_inserter(out), [](int elem) { return elem * 2; });
        std::for_each(out.begin(), out.end(), [](auto &&x) { printf("%d\n", x); });
    }

    void all_of() {
        auto ret = std::all_of(vec.begin(), vec.end(), [](auto &&x) {
            if (x == 1 || x == 2 || x ==3)
                return true;
            return false;
        });
        result(ret, __func__);
        ret = std::all_of(vec.begin(), vec.end(), [](auto &&x) {
            if (x == 1 || x != 2 || x ==3)
                return true;
            return false;
        });
        result(ret, __func__);
    }

    void any_of() {
        auto ret = std::any_of(vec.begin(), vec.end(), [](auto &&x) {
            if (x == 1)
                return true;
            return false;
        });
        result(ret, __func__);
        ret = std::any_of(vec.begin(), vec.end(), [](auto &&x) {
            return false;
        });
        result(ret, __func__);
    }

    void none_of() {
        auto ret = std::none_of(vec.begin(), vec.end(), [](auto &&x) {
            return false;
        });
        result(ret, __func__);
        ret = std::none_of(vec.begin(), vec.end(), [](auto &&x) {
            if (x == 1)
                return true;
            return false;
        });
        result(ret, __func__);
    }

    // std::for_each skip
    /* need clang compiler ...
    void for_each_n() {
        std::vector<int> vec = {2, 3, 4};
        std::for_each_n(vec.begin(), 2, [](auto &x) {
            printf("%d\n", x);
        });
    }
    */
    
} // namespace

int main(){
    //transform();
    //all_of();
    //any_of();
    //none_of();
    //for_each_n();

    return 0;
}