functional template

filter.cpp

#include <iostream>
#include <vector>
#include <list>

typedef std::vector<int> Ints;
using std::vector;

bool is_even(int x)
{
    return x % 2 == 0;
}

template<typename F, typename T>
T keep_if(F f, const T& xs)
{
    T ys;
    for (auto x : xs)
        if (f(x))
            ys.push_back(x);
    return ys;
}

int main()
{
    Ints xs = {0, 1, 2, 3, 4, 5};
  
    const auto ys = keep_if(is_even, xs);

    std::cout << "Results:";
    for (auto y : ys)
        std::cout << y << " ";
    std::cout << std::endl;

    std::list<int> xxs = { 5, 6, 7, 8, 9, 10};
    const auto yys = keep_if(is_even, xxs);

    std::cout << "Resultss2:";
    for (auto y : yys)
        std::cout << y << " ";
    std::cout << std::endl;
}