gistfile1.cpp

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

struct Person {
private:
	int age;
public:
	int getAge() const { return age; }
	Person() { age = rand() % 100 + 1; }
};

struct Wine {
private:
	int age;
public:
	int getAge() const { return age; }
	Wine() { age = rand() % 1000 + 1; }
};
	   
struct Rock {
private:
	long age;
public:
    long getAge() const {	return age;	}
	Rock() { age = rand(); }
};

template<typename R>
struct Foo {
public:
    template<typename T>
    R operator()(const T& obj) { return static_cast<R>(obj.getAge());	}
    typedef R result_type;
};


struct IteratorIterator {
	template<class T, typename Func>
  typename Func::result_type average(Func foo, T collection) {
    Func::result_type accum = 0;
		int size = 0; 
		for (typename T::const_iterator i = collection.begin(); i != collection.end(); ++i, size++) {
      typename T::const_reference ref = *i;
      accum += foo(ref);
    }
			
		return accum / size; // (size * 1.0)? Не выстрелить бы в ногу при приведении типов
	}
};

int _tmain(int argc, _TCHAR* argv[])
{	
	std::vector<Person> persons;
	std::vector<Wine> wine;
	std::vector<Rock> rocks;
	for (int i = 0; i < 10; i++) { 
		persons.push_back(Person::Person());
		wine.push_back(Wine::Wine());
		rocks.push_back(Rock::Rock());	
	}
	Foo<int> foo;
    Foo<long> foo2;
	IteratorIterator ii;
	printf("%d\n", ii.average(foo,persons));
	printf("%d\n", ii.average(foo,wine));
	printf("%d\n", ii.average(foo2,rocks));
	getchar();
	return 0;
}