containers/foursome.hpp - A 4-element collection


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

Note:This was originally called quadruple, but it turned out that both this and quad conflicted with some system headers on Solaris. So it eventually got renamed foursome.

Class Interface

The stlplus::foursome class looks like this:

template<typename T1, typename T2, typename T3, typename T4>
struct stlplus::foursome
  typedef T1 first_type;
  typedef T2 second_type;
  typedef T3 third_type;
  typedef T4 fourth_type;

  T1 first;
  T2 second;
  T3 third;
  T4 fourth;

  foursome(const T1& p1, const T2& p2, const T3& p3, const T4& p4);
  foursome(const foursome<T1,T2,T3,T4>& t2);

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

For example

// construct a foursome from elements
stlplus::foursome<unsigned,std::string,std::string,unsigned> f1(0, "zero", "help", 28);

// construct a foursome from another foursome
stlplus::foursome<unsigned,std::string,std::string> f2(f1);

// access the elements
std::cout << f1.first << ":" << f1.second << ":" << f1.third << ":" <<f1.fourth << std::endl;

Utility Functions

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

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

template<typename T1, typename T2, typename T3, typename T4>
foursome<T1,T2,T3,T4> make_foursome(const T1& first, const T2& second, const T3& third, const T4& fourth);

This can be used when assigning to an existing foursome:

stlplus::foursome<unsigned,std::string,std::string,unsigned> f1;
f1 = stlplus::make_foursome(0, "zero", "null", 28);

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

template<typename T1, typename T2, typename T3, typename T4>
bool operator == (const foursome<T1,T2,T3,T4>& left, const foursome<T1,T2,T3,T4>& right);

This can be used in any comparison:

if (f1 == f2)