#include <iostream>

template<typename Owner>
class Comparable;

template<typename Owner>
bool operator<(Comparable<Owner> const& left, Comparable<Owner> const& right)
{
    return left.owner().data() < right.owner().data();
}

template<typename Owner>
bool operator>(Comparable<Owner> const& left, Comparable<Owner> const& right)
{
    return left.owner().data() > right.owner().data();
}

template<typename Owner>
bool operator<=(Comparable<Owner> const& left, Comparable<Owner> const& right)
{
    return left.owner().data() <= right.owner().data();
}

template<typename Owner>
std::ostream& operator<<(std::ostream& s, Comparable<Owner> const& c)
{
    s << c.owner().name() << "(" << c.owner().data() << ")";
    return s;
}

template<typename Owner>
class Comparable
{
public:
    Owner const& owner() const
    {
        return *static_cast<Owner const * const>(this);
    }
};


class Timestamp : public Comparable<Timestamp>
{
  public:
    unsigned int _timestamp;

    unsigned int const& data() const
    {
        return _timestamp;
    }

    const char* name() const
    {
        return "Timestamp";
    }
};

class Interval : public Comparable<Interval>
{
  public:
    unsigned int _interval;

    unsigned int const& data() const
    {
        return _interval;
    }

    const char* name() const
    {
        return "Interval";
    }
};

/*

oleg (0) ~$ g++ test.cpp && ./a.out
Timestamp(5)<Timestamp(6) is true
Timestamp(5)>Timestamp(6) is false
Timestamp(5)<=Timestamp(6) is true

*/

int main(int, char*[])
{
    Timestamp lt, rt;
    Interval li, ri;
    lt._timestamp = 5;
    rt._timestamp = 6;
    li._interval = 7;
    ri._interval = 8;

    std::cout << lt << "<" << rt << " is " << (lt < rt ? "true" : "false") << std::endl;
    std::cout << lt << ">" << rt << " is " << (lt > rt ? "true" : "false") << std::endl;
    std::cout << lt << "<=" << rt << " is " << (lt <= rt ? "true" : "false") << std::endl;

    /*
      std::cout << lt << " < " << ri << " is incomparable " << (lt < ri ? "true" : "false") << std::endl;

      Error of compiler:

oleg (0) ~$ g++ test.cpp
test.cpp: In function ‘int main(int, char**)’:
test.cpp:87:68: error: no match for ‘operator<’ in ‘lt < ri’
test.cpp:87:68: note: candidate is:
test.cpp:7:6: note: template<class Owner> bool operator<(const Comparable<Owner>&, const Comparable<Owner>&)
test.cpp:7:6: note:   template argument deduction/substitution failed:
test.cpp:87:68: note:   deduced conflicting types for parameter ‘Owner’ (‘Timestamp’ and ‘Interval’)
    */

    return 0;
}