C++, Member function returning const reference to vector containing pointers to const objects

Question

I have a class with a member vector of pointers to objects. Now I want an accessor method to return a const reference to this vector. I also want the caller method to be unable to edit the objects pointed to by the vector's pointers, i.e. the pointers should point to const objects. Here is my erroneous code:

class Foo
{
private:
    vector<Foo*> myFoos;
public:
    const vector<const Foo*> &getMyFoos(void)
    {
        return myFoos; //Doesn't work since vector<Foo*> cannot be cast to vector<const Foo*>
    }
}

I have seen answers to similar questions where the solution is to make a copy of the vector myFoos where the copy is of the correct type. Is there anyway to do this without making a copy, since the myFoos vector may be very large?

You could return static_cast<Foo const *>(myFoos.data()) if the result will only be used for a short time, before you mutate the vector... — Kerrek SB
– Kerrek SB, Commented Apr 27, 2013 at 17:55
Return a pair of const iterators to begin and end. In C++11 teach for how to iterate over it as well. — Yakk - Adam Nevraumont
– Yakk - Adam Nevraumont, Commented Apr 27, 2013 at 17:58
@H2CO3: then you add a const Foo to your cast-to vector, and still later access it via the original vector and try changing it... BOOM. — n. m. could be an AI
– n. m. could be an AI, Commented Apr 27, 2013 at 17:58
Or use a type to wrap the pointers, where operator* and operator-> have adequate const versions. — dyp
– dyp, Commented Apr 27, 2013 at 18:07
Add a method to access the objects, instead of the vector: Foo const* getFoo(size_t i) const { return myFoos[i]; } -- Also a method to get the size. If your pointers cannot be null, return a reference instead. — Benjamin Lindley
– Benjamin Lindley, Commented Apr 27, 2013 at 18:11

Mikhail Veltishchev · Accepted Answer · 2013-08-21 08:50:19Z

0

Just add operator[] const to your Foo class:

const Foo& operator[] (size_t i) const {
    // you may add some range checking here
    return *myFoos[i];
}

answered Aug 21, 2013 at 8:50

Mikhail Veltishchev

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