Re: newobject and feature("ref")

That sounds like a bug to me. But feature("ref") won't automatically increment the refcount on objects returned from functions other than the ref-counted class's constructor, so I do not use feature("ref") at all in my programs. I use feature("unref") but not feature("ref"). Instead, I use a set of typemaps like this:

///////////////////////////////////////////////////////////////////////////
// Reference-counting typemaps for C# via AddRef() and ReleaseRef()
//
// Adds support for reference counting the specified type, assuming that the
// type includes AddRef() and ReleaseRef() methods. Unfortunately, this must
// be applied to every class in a ref-counted class hierarchy. Also, this
// macro changes many typemaps, and it may be incompatible with other macros
// that change the same typemaps.
//
// If you use %counted_obj on a base class then you get some, but not all,
// of the ref-counting logic in derived classes. Coincidentally, the most
// common mistake I make is to use %counted_obj on the base class "B" but
// forget to use it on a derived class "D". This mistake has two
// symptoms when dealing with pointers to D objects:
// 1. If some C++ method returns a D*, SWIG doesn't increment the ref-count,
//    but it doesn't decrement the ref-count when the wrapper is destroyed
//    either. Bottom line: either nothing bad happens, OR you might use the
//    object after it is destroyed.
// 2. If you allocate a D in C# with "new D()", AddRef() is not called, so
//    the refcount is zero. When that D instance is finalized, however,
//    ReleaseRef() is called. If some C++ code handles this D object, it
//    may be AddRef'd, then ReleaseRef'd, causing the object to be freed
//    prematurely.
%define %counted_obj(TYPE)
        // The 'ref' and 'unref' features enable reference counting on 'new'
        // and 'delete' only (in C#, delete is called for garbage
        // collection.) These are nice features because they apply to a whole
        // type hierarchy. Unfortunately, they are not enough. The refcount
        // must be incremented whenever a function returns TYPE*, so we use
        // the 'out' typemap to accomplish that. Since the 'out' typemap
        // applies to the 'new' operator, we cannot use %feature("ref") to
        // add a reference at the same time, for it would cause a second
        // increment. Unfortunately, typemaps do not apply to entire
        // inheritance hierarchies, which is why %counted_obj must be used
        // on every class in a hierarchy.
        %feature("unref") TYPE "$this->ReleaseRef(); // unref"
        %typemap(csin) TYPE "$csinput.Ptr"
       
        %typemap(in)       TYPE* %{ $1 = (TYPE*)$input; %}
        %typemap(varin)    TYPE* %{ $1 = (TYPE*)$input; %}
        %typemap(memberin) TYPE* %{ $1 = (TYPE*)$input; %}
        %typemap(out, null="NULL") TYPE* %{
                if ($1 != NULL) $1->AddRef(); // C# side is responsible for releasing the reference
                $result = $1;
        %}
        %typemap(csout, excode=SWIGEXCODE) TYPE* {
                IntPtr cPtr = $imcall;$excode
                if (cPtr == IntPtr.Zero)
                  return null;
                return new $csclassname(cPtr, true);
          }
        %typemap(csvarout, excode=SWIGEXCODE2) TYPE* %{
                get {
                  IntPtr cPtr = $imcall;$excode
                  if (cPtr == IntPtr.Zero)
                    return null;
                  return new $csclassname(cPtr, true);
                } %}
%enddef

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