Call delegate from C++

[Nicholas Wilson via Digitalmars-d-learn]

How do you pass a delegate to a c++ function to be called by it?
The function to pass the delegate to is:

extern (C++) int
fakeEntrypoint(
    extern(C++) void function(void* /*delegate's context*/) func,
    void* /*delegate's context*/ arg);


What I want is:

int entrypoint(scope void delegate() func)
{
    return fakeEntrypoint(
                // for some reason func.funcptr is void function()
                cast(void function(void*))func.funcptr,
                func.ptr);
}

but that fails with

cannot pass argument cast(void function(void*))func.funcptr of 
type
void function(void*) to parameter extern (C++) void 
function(void*) func