c++ lambda + stl(filter, sort, remove_if, reduce, vector)

lambda 함수는 stl과 결합하면 상당히 좋은 성능을 보인다.

#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <utility>
#include <execution>
 
class Cat
{
public:
    explicit Cat(int age) : mAge{ age } {};
    ~Cat() noexcept { std::cout << "Cat destructor finished " << std::endl; };
    int age() const
    {
        return mAge;
    };
    void speak() const
    {
        std::cout << "meow" << std::endl;
    };
    void test() const
    {
        // class 안에서 &를 붙이면 this를 capture하는 것임(this는 object의 point)
        //auto lambda = [&]()
        // explicit하게 capture를 넘겨주는게 좋다.
        auto lambda = [this] ()
        {
            std::cout << "lambdaFunction" << std::endl;
            std::cout << mAge << std::endl;
            // std::cout << this->mAge << std::endl;
            
            speak();
        };
        lambda();
    };
private:
    int mAge;
};
 
int main()
{
    Cat kitty{ 1 };
    kitty.test();
 
    std::vector<int> nums{ 1,2,3,4,5,6,7,8,9,10 };
    auto lambdaAdd10 = [](int& n)
    {
        n += 10;
    };
    int n = 10;
    lambdaAdd10(n);
    std::cout << n << std::endl;
    ///////////////////////////////////
    //        for each stl 적용하기     //
    ///////////////////////////////////
    //std::for_each(nums.begin(), nums.end(), lambdaAdd10);
    // lambda의 장점 -> unanimous 함수로 가능
    std::for_each(nums.begin(), nums.end(), [](int& n) 
    {
            n += 10;
    });
    for (int num : nums)
    {
        std::cout << num << " ";
    }
    std::cout << std::endl;
    ///////////////////////////////////
    //        for each stl 적용하기     //
    ///////////////////////////////////
    std::vector<int> nums2{ 1,2,3,4,5,6,7,8,9,10 };
    auto filterOdd = [](int n)
    {
        return n % 2 == 1;
    };
    //nums2.erase(std::remove_if(nums2.begin(), nums2.end(), filterOdd));
    nums2.erase(std::remove_if(nums2.begin(), nums2.end(), [](int n)
        {
            return n % 2 == 1;
        }), nums2.end());
 
    std::cout << "Odd erase" << std::endl;
    for (int num: nums2) {
        std::cout << num << " ";
    }
    std::cout << std::endl;
    ///////////////////////////////////
    //        sorting 적용하기     //
    ///////////////////////////////////
    std::vector<int> nums3{ 10,5,4,7,9,8,3,2,1 };
    std::sort(nums3.begin(), nums3.end(), [](int a, int b)
    {
            //return a < b;
            return std::abs(a - 5) < std::abs(b - 5);
    });
    std::cout << "sorting" << std::endl;
    for (int num : nums3) {
        std::cout << num << " ";
    }
 
    ///////////////////////////////////
    //        reduce 적용하기     //
    ///////////////////////////////////
    std::vector<int> nums4{ 10,5,4,7,9,8,3,2,1,6 };
    int sum = std::reduce(nums4.begin(), nums4.end(), 0, [](int a, int b)
        {
            return a + b;
        });
    std::cout << std::endl;
    std::cout << "sum reduce" << std::endl;
    std::cout << sum << std::endl;
 
    int mul = std::reduce(nums4.begin(), nums4.end(), 1, [](int a, int b)
        {
            return a*b;
        });
    std::cout << std::endl;
    std::cout << "multiply reduce" << std::endl;
    std::cout << mul << std::endl;
    
 
    ///////////////////////////////////
    //        class에 sort 적용하기    //
    ///////////////////////////////////
    Cat acat{ 10 };
    std::cout << "고양이 나이 : " << acat.age() << std::endl;
 
    std::vector<Cat> cats;
    for (int i = 100; i > 0; i--)
    {
        cats.push_back(Cat{ i });
        std::cout << "cat " << i << "번째 고양이가 입력되었습니다" << std::endl;
    };
 
    std::sort(cats.begin(), cats.end(), [](Cat& a, Cat& b) {
        return a.age() < b.age();
        }
    );
    
    for (Cat cat : cats)
    {
        std::cout << cat.age() << std::endl;
    };
 
    return 0;
}