remove（）STL多继承的处理

Question

We have created three STL and STL-inherited data types for use in a clustering algorithm:

typedef std::vector<double>Point;   // A list of parameters (a single observation)

struct Cluster : std::list<Point> {   // A list of Points
   // Additional member variables
   Point centroid;
   bool centroid_valid;
   bool sort_valid;
   // Cluster functions omitted
};

struct Universe : std::list<Cluster> {   // A list of Clusters
   // No member variables
   // Universe functions omitted
};

This is an attempt to fully utilize the STL so nothing is new 'd into existence. The concern is having to do with the nature of subordinated STL functionality, specifically:

If we were to remove() a Cluster element from a Universe list, would the STL handle not only the deletion (and memory management) of all Point s in the Cluster to be removed, but also the deletion-handling of all member variables?

Note: all member functions are relatively simple, with no static operations.

Answer 1

If we were to remove() a Cluster element from a Universe list, would the STL handle not only the deletion (and memory management) of all Points in the Cluster to be removed, but also the deletion-handling of all member variables?

Yes it will because it operates on Cluster objects and removing it will remove all its fields. But inheritance from standard containers is considered to be a bad practice because they do not have a virtual destructor. It is better to store list of Points in a Cluster as a property.

Answer 2

wrong:

typedef std::vector<double>Point;   // A list of parameters (a single observation)

struct Cluster : std::list<Point> {   // A list of Points
   // Additional member variables
   Point centroid;
   bool centroid_valid;
   bool sort_valid;
   // Cluster functions omitted
};

right:

typedef std::vector<double>Point;   // A list of parameters (a single observation)

struct Cluster {   // A list of Points

   std::list<Point> points;

   // Additional member variables
   Point centroid;
   bool centroid_valid;
   bool sort_valid;
   // Cluster functions omitted
};

When you inherit from a class, you are inherently guaranteeing that all of its member functions will behave sanely when called against your class.

The problem for you is that the 'additional member variables' are cached observations of the points. If you erase or insert a point, these cached observations will be out of sync, and therefore wrong .

If you want Cluster to have the same interface as std::list, then you must implement that interface, call into the member points and update (or mark as invalid) the cached observations.