Efficient alternatives for exposing a Collection

Question

In C++, what alternatives do I have for exposing a collection, from the point of view of performance and data integrity?

My problem is that I want to return an internal list of data to the caller, but I don't want to generate a copy. Thant leaves me with either returning a reference to the list, or a pointer to the list. However, I'm not crazy about letting the caller change the data, I just want to let it read the data.

• Do I have to choose between performance and data integrity?
• If so, is in general better to go one way or is it particular to the case?
• Are there other alternatives?

Answer 1

RichQ's answer is a reasonable technique, if you're using an array, vector, etc.

If you're using a collection that isn't indexed by ordinal values... or think you might need to at some point in the near future... then you might want to consider exposing your own iterator type(s), and associated begin()/end() methods:

class Blah
{
public:
   typedef std::vector<mydata> mydata_collection;
   typedef myDataCollection::const_iterator mydata_const_iterator;

   // ...

   mydata_const_iterator data_begin() const 
      { return myPreciousData.begin(); }
   mydata_const_iterator data_end() const 
      { return myPreciousData.end(); }

private:
   mydata_collection  myPreciousData;
};

...which you can then use in the normal fashion:

Blah blah;
for (Blah::mydata_const_iterator itr = blah.data_begin();
   itr != blah.data_end();
   ++itr)
{
   // ...
}