Hi Fabian,

This is a first try to generalize COM implementations.
I find it useful to not repeat all that code for every
new implementation.

Feedback appreciated, can we go that route?

diff --git a/include/wine/com.h b/include/wine/com.h
new file mode 100644
index 0000000000..2f73bfcbd0
--- /dev/null
+++ b/include/wine/com.h

I'm skeptical about this being general COM helper. A header just for class factory could be better.

@@ -0,0 +1,256 @@
+/*
+ * COM helper functions
+ *
+ * Copyright 2018 Fabian Maurer
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#ifndef __WINE_WINE_COM_H
+#define __WINE_WINE_COM_H
+
+#define COBJMACROS
+#include "unknwn.h"
+
+#include <stdarg.h>
+#include "windef.h"
+#include "winbase.h"
+#include "winuser.h"
+#include "winreg.h"
+#include "rpcproxy.h"
+
+#include "wine/debug.h"
+
+#ifdef __WINE_WINE_TEST_H
+#error This file should not be used in Wine tests
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static HINSTANCE instance_dll;
+
+#ifdef WINE_COM_MAIN
+
+typedef struct
+{
+    const CLSID *clsid;
+    HRESULT (*pfnCreateInstance)(IUnknown *unk_outer, void **ppobj);
+} com_object_creation_info;

+
+typedef struct
+{
+    IClassFactory IClassFactory_iface;
+
+    LONG ref;

+    HRESULT (*pfnCreateInstance)(IUnknown *unk_outer, void **ppobj);

+} IClassFactoryImpl;

+
+static inline BOOL WINAPI com_main(HINSTANCE instance, DWORD reason, LPVOID reserved)
+{
+    TRACE("(0x%p, %d, %p)\n", instance, reason, reserved);
+
+    switch (reason)
+    {
+        case DLL_WINE_PREATTACH:
+            return FALSE;    /* prefer native version */
+        case DLL_PROCESS_ATTACH:
+            DisableThreadLibraryCalls(instance);
+            instance_dll = instance;
+            break;
+    }
+
+    return TRUE;
+}

+static HRESULT WINAPI classfactory_LockServer(IClassFactory *iface, BOOL dolock)
+{
+    IClassFactoryImpl *impl = impl_from_IClassFactory(iface);
+    FIXME("(%p)->(%d), stub!\n", impl, dolock);

+    return S_OK;
+}
+
+static const IClassFactoryVtbl classfactory_Vtbl =
+{
+    classfactory_QueryInterface,
+    classfactory_AddRef,
+    classfactory_Release,
+    classfactory_CreateInstance,
+    classfactory_LockServer
+};
+
+HRESULT WINAPI com_get_class_object(const com_object_creation_info *object_creation, int object_creation_length,
+        REFCLSID rclsid, REFIID riid, void **ppv)
+{
+    unsigned int i;
+    IClassFactoryImpl *factory;
+
+    TRACE("(%s,%s,%p)\n", debugstr_guid(rclsid), debugstr_guid(riid), ppv);
+
+    if (!IsEqualGUID(&IID_IClassFactory, riid)
+         && !IsEqualGUID( &IID_IUnknown, riid))
+        return E_NOINTERFACE;
+
+    for (i = 0; i < object_creation_length; i++)
+    {
+        if (IsEqualGUID(object_creation[i].clsid, rclsid))
+            break;
+    }
+
+    if (i == object_creation_length)
+    {
+        FIXME("%s: no class found.\n", debugstr_guid(rclsid));
+        return CLASS_E_CLASSNOTAVAILABLE;
+    }
+
+    factory = HeapAlloc(GetProcessHeap(), 0, sizeof(*factory));
+    if (factory == NULL)
+        return E_OUTOFMEMORY;
+
+    factory->IClassFactory_iface.lpVtbl = &classfactory_Vtbl;
+    factory->ref = 1;
+
+    factory->pfnCreateInstance = object_creation[i].pfnCreateInstance;
+
+    *ppv = &factory->IClassFactory_iface;
+    return S_OK;
+}