Q:

MIDL (Constant) References

Are there no constant references in MIDL method declarations????
eg.
[id(1), helpstring("My Method")]
HRESULT MyMethod(
    [in] IID & const rclsid
);

for
HRESULT MyMethod(
    IID const &rclsid
);

A:

MIDL doesn't really support reference parameters, it only supports "in" and "out" parameters.  So if you DO pass in a reference, it's just syntactic sugar for a pointer to the value (the issue is observability - if you have a callback function or interface in our method signature, changes to a reference would be observable from the callback, but changes to an [out] parameter aren't visible until the function returns.
In addition, the difference between "& const" and "const &" are lost.  If you look at the definition of REFGUID, you'll see that they only use one form of "const" for C++ code:
#ifdef __midl_proxy
#define __MIDL_CONST
#else
#define __MIDL_CONST const
#endif

#ifndef _REFGUID_DEFINED
#define _REFGUID_DEFINED
#ifdef __cplusplus
#define REFGUID const GUID &
#else
#define REFGUID const GUID * __MIDL_CONST
#endif
#endif

