Exporting ative type compiled with /CLR

[Jesper Schmidt]

How do I export native types compiled with option /CLR (MSIL code)? I
am able to export MSIL code with __declspec(dllexport) as long as no
CLR data is involved, but I get the following compiler error if I try
to pass CLR data to a MSIL function.

"__declspec(dllexport) cannot be applied to a function with the
__clrcall calling convention"

I have noticed that a MSIL function exported with __declspec(dllexport)
involves a managed transition even when it is called from another MSIL
module. I think, I do understand why this is necessary, but there must
be a better way to "export" native types between MSIL modules. I have
tried with #using DLL, but apparently, it does not work for native
types. Below is a code example, which illustrates what I am trying to
do.

--------------------------
Library code (library.dll)
--------------------------
Header file
-----------
class base {
public:
virtual ~base() {}
virtual void write(unsigned char);
};

class derived : public base {
private:
gcroot<System::IO::Stream^out_;
void write(unsigned char);
public:
derived(System::IO::Stream^ out);
};

-----------
Source file
-----------
derived::derived(System::IO::Stream^ out) : out_(out) {}

void derived::write(unsigned char ch)
{
out_->WriteByte(ch);
}

--------------------------
Program code (program.exe)
--------------------------
#include "library.h"

#using <library.dll// desperate attempt

int main()
{
base* p = new derived(gcnew System::IO::FileStream("a.bin",
System::IO::FileMode::Create));
p->write('a');
delete p;
}
Thanks in advance
Jesper