small function timer in c++11

example.cpp

#include <iostream>
#include <chrono>
#include <thread>
#include "timer.hpp"
int main(){
    std::chrono::milliseconds  nap( 2000 );
    std::cout<<timer([&](){std::this_thread::sleep_for( nap );}).count()<<std::endl;
}

timer.hpp

#include <chrono>
template<class fn>
std::chrono::milliseconds timer(fn f){
    auto t1 = std::chrono::high_resolution_clock::now();
    f();
    auto t2 = std::chrono::high_resolution_clock::now();
    return duration_cast<std::chrono::milliseconds>(t2-t1);
}