lambda functions

main.cxx

#include "template.h"
#include <vector>
#include <iostream>

int main(){
    std::vector<int> V{1, 2, 3, 4, 5}; 
    std::vector<int> filtered = filter( [](int i){return i %2 == 0;}, V); 
    for( auto f : filtered ){
        std::cout << f << std::endl;
    } 
    
    int j = 4;
    // The ampersand makes local variables visible inside the lambda.
    std::vector<int> filtered2 = filter( [&](int i){return i > j;}, V); 
    for( auto f : filtered2 ){
        std::cout << f << std::endl;
    } 
    
}

template.h

#include <vector>

template<typename func, typename T>
std::vector<T> filter( func f, std::vector<T> arr)
{
    std::vector<T> ret;
    for (auto i : arr ){
        if ( f(i) ){
            ret.push_back( i );
        }   
    }   
    return ret;
}