Introduction

The stlplus::triple class is similar to the std::pair class except it contains three objects, each of which can be of a different type. This class and its family of collection classes pair/triple/foursome are useful in themselves but are probably most useful in building data structures.

Class Interface

The stlplus::triple class looks like this:

template<typename T1, typename T2, typename T3>
struct stlplus::triple
{
  typedef T1 first_type;
  typedef T2 second_type;
  typedef T3 third_type;

  T1 first;
  T2 second;
  T3 third;

  triple(void);
  triple(const T1& p1, const T2& p2, const T3& p3);
  triple(const triple<T1,T2,T3>& t2);
};

The class contains three elements called first, second and third. The constructor initialises the three elements, either from individual values or from another triple.

For example

// construct a triple from elements
stlplus::triple<unsigned,std::string,std::string> t1(0, "zero", "null");

// construct a triple from another triple
stlplus::triple<unsigned,std::string,std::string> t2(t1);

// access the elements
std::cout << t1.first << ":" << t1.second << ":" << t1.third << std::endl;

Utility Functions

The header also provides utilities to help create triples and to compare them.

The stlplus::make_triple is analagous to the STL's std::make_pair:

template<typename T1, typename T2, typename T3>
triple<T1,T2,T3> stlplus::make_triple(const T1& first, const T2& second, const T3& third);

This can be used when assigning to an existing triple:

stlplus::triple<unsigned,std::string,std::string> t1;
t1 = stlplus::make_triple(0, "zero", "null");

The operator== template is provided to make it easy to compare two triples, provided they have the same element types:

template<typename T1, typename T2, typename T3>
bool operator == (const stlplus::triple<T1,T2,T3>& left, const stlplus::triple<T1,T2,T3>& right);

This can be used in any comparison:

if (t1 == t2)
{
  ...
}