On Monday, 13 November 2023 at 16:23:05 UTC, Tim wrote:

Wow, it really was that simple all along. Thanks for the tip!

On Monday, 13 November 2023 at 16:09:51 UTC, Guillaume Piolat wrote:

Seconded, though I didn't follow all of it...

On Monday, 13 November 2023 at 16:52:06 UTC, Paul Backus wrote:

That's not a complete solution. If you template the visitor and have some member functions that override the extern(C++) base class methods, then you will still end up with errors if you use any types that use non-mapable C++ types because of the mangling. For example:

extern(C++) class DMDVisitor
{
    void visit(Expression e) {}
}

class MyVisitor(T) : DMDVisitor
{
    T field;
    extern(C++) override void visit(Expression e) {}   // troubled line
}

Instantiating MyVisitor with a string type will issue an error at the troubled line because the mangler needs to take into account the template instance. Since C++ has no dynamic array correspondent you essentially cannot call MyVisitor.visit from C++ and therefore the compiler issues an error.

However, if you don't use templated visitors you are fine, you can just mark your introducing functions/fields as extern(D) and even if the class is extern(C++) it will work.