Implementing GetEnumerator in C++

Question

In C# i have the following class and it compiles just fine:

class CustomItem { }

class CustomList : IList<CustomItem>
{
    public CustomItem this[int index]
    {
        get { return null; }
        set { throw new NotImplementedException(); }
    }
    public void CopyTo(CustomItem[] array, int arrayIndex)
    {
    }

    public int Count { get { return 10; } }
    public int IndexOf(CustomItem item) { throw new NotImplementedException(); }
    public void Insert(int index, CustomItem item) { throw new NotImplementedException(); }
    public void RemoveAt(int index) { throw new NotImplementedException(); }
    public void Add(CustomItem item) { throw new NotImplementedException(); }
    public void Clear() { throw new NotImplementedException(); }
    public bool Contains(CustomItem item) { throw new NotImplementedException(); }
    public bool IsReadOnly { get { return true; } }
    public bool Remove(CustomItem item) { throw new NotImplementedException(); }

    public IEnumerator<CustomItem> GetEnumerator() { throw new NotImplementedException(); }
    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    { throw new NotImplementedException(); }
}

When i try the same in C++ i get several compiler errors:

ref class CustomItemValue { };

typedef CustomItemValue^ CustomItem;

ref class CustomList : public IList<CustomItem>
{
public:
    property CustomItem default[int]
    {
        virtual CustomItem get(int index) { return nullptr; }
        virtual void set(int index, CustomItem value) {}
    }
    virtual void CopyTo(array<CustomItem>^ array, int arrayIndex)
    {
    }

    property int Count { virtual int get() { return 10; } }
    virtual int IndexOf(CustomItem item) { throw gcnew NotImplementedException(); }
    virtual void Insert(int index, CustomItem item) { throw gcnew NotImplementedException(); }
    virtual void RemoveAt(int index) { throw gcnew NotImplementedException(); }
    virtual void Add(CustomItem item) { throw gcnew NotImplementedException(); }
    virtual void Clear() { throw new NotImplementedException(); }
    virtual bool Contains(CustomItem item) { throw gcnew NotImplementedException(); }
    property bool IsReadOnly { virtual bool get() { return true; } }
    virtual bool Remove(CustomItem item) { throw gcnew NotImplementedException(); }

    virtual IEnumerator<CustomItem>^ GetEnumerator() { throw gcnew NotImplementedException(); }
    virtual System::Collections::IEnumerator^ GetEnumerator()
    { throw gcnew NotImplementedException(); }
};

The error messages from the compiler are:

.\mc.cpp(38) : error C2556: 'System::Collections::IEnumerator ^CustomList::GetEnumerator(void)' : overloaded function differs only by return type from 'System::Collections::Generic::IEnumerator ^CustomList::GetEnumerator(void)' with [ T=CustomItem ] .\mc.cpp(36) : see declaration of 'CustomList::GetEnumerator' .\mc.cpp(38) : error C2371: 'CustomList::GetEnumerator' : redefinition; different basic types .\mc.cpp(36) : see declaration of 'CustomList::GetEnumerator'

Can anyone help me with this?

Answer 1

You need to use the Microsoft specific explicit override syntax for to override both GetEnumerator() methods:

virtual System::Collections::IEnumerator^ GetEnumerator2() = System::Collections::IEnumerable::GetEnumerator
{ throw gcnew NotImplementedException(); }

virtual IEnumerator<CustomItem>^ GetEnumerator()
{ throw gcnew NotImplementedException(); }

Note that I renamed the non-generic GetEnumerator method to GetEnumerator2 then specifies that it overrides System::Collections::IEnumerable::GetEnumerator. You can find out more about explicit override in here

Answer 2

Well you have a clue in th error message. your GetEnumerator method returns System::Collections::IEnumerator^ while there is another method to this class that returns System::Collections::Generic::IEnumerator^ , this method is probably inherited from IList class.

Try to replace the return value with System::Collections::Generic::IEnumerator^.