C++/CLI Generic::Dictionary Declaration Syntax

I'm been curious about the declaration syntax of Collections::Generic::Dictionary class in C++/CLI.

Normally we declare a reference in开发者_JS百科 a class and initialize it:

public ref class CDemo {
    private: ClassA ^ m_InstanceA;

    // Why the absence of '^'.
    private: Dictionary<int, int> m_Dic;

    CDemo() : 
        m_InstanceA(gcnew ClassA()),   
        m_Dic(gcnew Dictionary<int, int>()) 
    {...}
};

Could someone explains please why should the '^' absent there?

What's more, if I were to use the dictionary above as a TValue of another dictionary, I have to declare it like this:

Dictionary<T, Dictionary<T, T>^ > m_Dic;  // A '^' in the TValue parameter, which is           
                                          // normal, but same question as above,
                                          // I don't have to declare m_Dic as ^ ?

Thanks.

This is not specific to Dictionary. This syntax is a way to help map C++ semantics onto managed types. In general:

ref class A
{
   ReferenceType m_obj;
}; 

is roughly equivalent to

class A : IDisposable
{
  private ReferenceType m_obj;
  void Dispose() { m_obj.Dispose(); }
}

in C# if ReferenceType implements IDisposable. It is perfectly possible to write

ref class A
{
   ReferenceType^ m_obj;
};

This does not have the implicit IDisposable support. The other difference is that you can return a ReferenceType^ from a method, this is not supported with just plain ReferenceType. For example:

ref class A
{ 
   ReferenceType^ m_obj;
   ReferenceType^ GetIt() { return m_obj; }
};

will compile,

ref class A
{
   ReferenceType m_obj;
   ReferenceType GetIt() { return m_obj; }  // won't compile
   ReferenceType^ OtherGetIt() { return m_obj; } // neither will this
};

A similar distinction is provided for automatic (stack variables)

      ReferenceType local;
      local.Stuff();

is desugared by the compiler to

      try {
        ReferenceType^ local = gcnew ReferenceType();
        local->Stuff();
      } finally {
        delete local; // invokes Dispose() (~ReferenceType)
      }

These features bring the familiar idiom of RAII to C++/CLI with managed types.

EDIT:

Yes, the Dispose method of IDisposable is analogous to a C++ destructor. If ReferenceType doesn't implement IDisposable (doesn't have a dtor), and it is the only member, A will also not implement IDisposable (not have an implicit dtor). In C++/CLI you implement IDisposable by providing a dtor (for managed types).