Added wxCOMPtr<> helper class.

This allows to avoid error-prone manual AddRef() and Release() calls when
writing COM code in wxMSW.

See #11401.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71200 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/private/comptr.h

@@ -0,0 +1,130 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/msw/private/comptr.h
+// Purpose:     Smart pointer for COM interfaces.
+// Author:      PB
+// Created:     2012-04-16
+// RCS-ID:      $Id: $
+// Copyright:   (c) 2012 wxWidgets team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_MSW_PRIVATE_COMPTR_H_
+#define _WX_MSW_PRIVATE_COMPTR_H_
+
+// ----------------------------------------------------------------------------
+// wxCOMPtr: Minimalistic a smart pointer for use with COM interfaces.
+// ----------------------------------------------------------------------------
+
+template <class T>
+class wxCOMPtr
+{
+public:
+    typedef T element_type;
+
+    wxCOMPtr()
+        : m_ptr(NULL)
+    {
+    }
+
+    wxEXPLICIT wxCOMPtr(T* ptr)
+        : m_ptr(ptr)
+    {
+        if ( m_ptr )
+            m_ptr->AddRef();
+    }
+
+    wxCOMPtr(const wxCOMPtr& ptr)
+        : m_ptr(ptr.get())
+    {
+        if ( m_ptr )
+            m_ptr->AddRef();
+    }
+
+    ~wxCOMPtr()
+    {
+        if ( m_ptr )
+            m_ptr->Release();
+    }
+
+    void reset(T* ptr = NULL)
+    {
+        if ( m_ptr != ptr)
+        {
+            if ( ptr )
+                ptr->AddRef();
+            if ( m_ptr )
+                m_ptr->Release();
+            m_ptr = ptr;
+        }
+    }
+
+    wxCOMPtr& operator=(const wxCOMPtr& ptr)
+    {
+        reset(ptr.get());
+        return *this;
+    }
+
+    wxCOMPtr& operator=(T* ptr)
+    {
+        reset(ptr);
+        return *this;
+    }
+
+    operator T*() const
+    {
+        return m_ptr;
+    }
+
+    T& operator*() const
+    {
+        return *m_ptr;
+    }
+
+    T* operator->() const
+    {
+        return m_ptr;
+    }
+
+    // It would be better to forbid direct access completely but we do need
+    // for QueryInterface() and similar functions, so provide it but it can
+    // only be used to initialize the pointer, not to modify an existing one.
+    T** operator&()
+    {
+        wxASSERT_MSG(!m_ptr,
+                     wxS("Can't get direct access to initialized pointer"));
+
+        return &m_ptr;
+    }
+
+    T* get() const
+    {
+        return m_ptr;
+    }
+
+    bool operator<(T* ptr) const
+    {
+        return get() < ptr;
+    }
+
+private:
+    T* m_ptr;
+};
+
+// Define a helper for the macro below: we just need a function taking a
+// pointer and not returning anything to avoid warnings about unused return
+// value of the cast in the macro itself.
+namespace wxPrivate { void PPV_ARGS_CHECK(void*) { } }
+
+// Takes the interface name and a pointer to a pointer of the interface type
+// and expands into the IID of this interface and the same pointer but after a
+// type-safety check.
+//
+// This is similar to the standard IID_PPV_ARGS macro but takes the pointer
+// type instead of relying on the non-standard Microsoft __uuidof().
+#define wxIID_PPV_ARGS(IType, pType) \
+    IID_##IType, \
+    (wxPrivate::PPV_ARGS_CHECK(static_cast<IType*>(*pType)), \
+     reinterpret_cast<void**>(pType))
+
+#endif // _WX_MSW_PRIVATE_COMPTR_H_
+