One of the usage of operator()

// operator_callable.cpp
#include <iostream>

using namespace std;

template <typename T>
struct Print {
    void operator() (const T& msg) const
    {
        cout << msg << " ";
    }
};

template <typename T, typename Func>
void ForEach(T* begin, T* end, const Func& func)
{
    while (begin != end) {
        func(*begin++);
    }
}


int main(int argc, char **argv) 
{
    int array[] = {10, 11, 23, 25, 30};
    ForEach(array, array + 5, Print<int>{});
    return 0;
}

Compile implementation

g++ -o operator_callable operator_callable.cpp -std=c++11