I’m very new to c++20 modules and i’m trying this:

VariantFunctions.ixx

export module VariantFunctions;

struct tagVARIANT;  // Forward declaration of VARIANT type
typedef struct tagVARIANT VARIANT;

export bool IsNonZeroI4x(const VARIANT & v) noexcept;

I’m trying to call this function from Win32 code which uses MFC like this:

VARIANT v;
VariantInit(&v);
IsNonZeroI4x(v);

The compiler (Visual Studio 2022, 17.11.3) tells me:

error C2664: ‘bool IsNonZeroI4x(const VARIANT &) noexcept’: cannot convert argument 1 from ‘VARIANT’ to ‘const VARIANT &’

I can write a similar function that takes a simple type, like a long in the place of a VARIANT, but I need to understand why the code above doesn’t work.

I’ve tried to use #include <oleauto> in the .ixx file, but there’s so many module-incompatible things in that header that it’s not possible, hence why I pondered a forward declaration.