Defining operator += (and -=) is probably the most important method to implement arbitrary kinds of user defined aggregations. An alternative way to choose a desired aggregation is to instantiate an interval_map class template with an appropriate aggregation functor. For the most common kinds of aggregation the icl provides such functors as shown in the example.

Example partys_tallest_guests.cpp also demonstrates the difference between an interval_map that joins intervals for equal associated values and a split_interval_map that preserves all borders of inserted intervals.

// The next line includes <boost/date_time/posix_time/posix_time.hpp>
// and a few lines of adapter code.
#include <boost/icl/ptime.hpp>
#include <iostream>
#include <boost/icl/interval_map.hpp>
#include <boost/icl/split_interval_map.hpp>

using namespace std;
using namespace boost::posix_time;
using namespace boost::icl;


// A party's height shall be defined as the maximum height of all guests ;-)
// The last parameter 'inplace_max' is a functor template that calls a max 
// aggregation on overlap.
typedef interval_map<ptime, int, partial_absorber, less, inplace_max>
    PartyHeightHistoryT;

// Using a split_interval_map we preserve interval splittings that occurred via insertion.
typedef split_interval_map<ptime, int, partial_absorber, less, inplace_max>
    PartyHeightSplitHistoryT;

void partys_height()
{
    PartyHeightHistoryT tallest_guest;

    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 19:30"),
          time_from_string("2008-05-20 23:00")),
        180); // Mary & Harry: Harry is 1,80 m tall.

    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 20:10"),
          time_from_string("2008-05-21 00:00")),
        170); // Diana & Susan: Diana is 1,70 m tall.

    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 22:15"),
          time_from_string("2008-05-21 00:30")),
        200); // Peters height is 2,00 m

    PartyHeightHistoryT::iterator height_ = tallest_guest.begin();
    cout << "-------------- History of maximum guest height -------------------\n";
    while(height_ != tallest_guest.end())
    {
        discrete_interval<ptime> when = height_->first;
        // Of what height are the tallest guests within the time interval 'when' ?
        int height = (*height_++).second;
        cout << "[" << first(when) << " - " << upper(when) << ")"
             << ": " << height <<" cm = " << height/30.48 << " ft" << endl;
    }

}

// Next we are using a split_interval_map instead of a joining interval_map
void partys_split_height()
{
    PartyHeightSplitHistoryT tallest_guest;

    // adding an element can be done wrt. simple aggregate functions
    // like e.g. min, max etc. in their 'inplace' or op= incarnation
    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 19:30"),
          time_from_string("2008-05-20 23:00")),
        180); // Mary & Harry: Harry is 1,80 m tall.

    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 20:10"),
          time_from_string("2008-05-21 00:00")),
        170); // Diana & Susan: Diana is 1,70 m tall.

    tallest_guest +=
      make_pair(
        discrete_interval<ptime>::right_open(
          time_from_string("2008-05-20 22:15"),
          time_from_string("2008-05-21 00:30")),
        200); // Peters height is 2,00 m

    PartyHeightSplitHistoryT::iterator height_ = tallest_guest.begin();
    cout << "\n";
    cout << "-------- Split History of maximum guest height -------------------\n";
    cout << "--- Same map as above but split for every interval insertion.  ---\n";
    while(height_ != tallest_guest.end())
    {
        discrete_interval<ptime> when = height_->first;
        // Of what height are the tallest guests within the time interval 'when' ?
        int height = (*height_++).second;
        cout << "[" << first(when) << " - " << upper(when) << ")"
             << ": " << height <<" cm = " << height/30.48 << " ft" << endl;
    }

}


int main()
{
    cout << ">>Interval Container Library: Sample partys_tallest_guests.cpp  <<\n";
    cout << "------------------------------------------------------------------\n";
    partys_height();
    partys_split_height();
    return 0;
}

// Program output:
/*-----------------------------------------------------------------------------
>>Interval Container Library: Sample partys_tallest_guests.cpp  <<
------------------------------------------------------------------
-------------- History of maximum guest height -------------------
[2008-May-20 19:30:00 - 2008-May-20 22:15:00): 180 cm = 5.90551 ft
[2008-May-20 22:15:00 - 2008-May-21 00:30:00): 200 cm = 6.56168 ft

-------- Split History of maximum guest height -------------------
--- Same map as above but split for every interval insertion.  ---
[2008-May-20 19:30:00 - 2008-May-20 20:10:00): 180 cm = 5.90551 ft
[2008-May-20 20:10:00 - 2008-May-20 22:15:00): 180 cm = 5.90551 ft
[2008-May-20 22:15:00 - 2008-May-20 23:00:00): 200 cm = 6.56168 ft
[2008-May-20 23:00:00 - 2008-May-21 00:00:00): 200 cm = 6.56168 ft
[2008-May-21 00:00:00 - 2008-May-21 00:30:00): 200 cm = 6.56168 ft
-----------------------------------------------------------------------------*/