[Issue 12854] New: Cannot interface to C++ code with const class pointers

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12854

          Issue ID: 12854
           Summary: Cannot interface to C++ code with const class pointers
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P1
         Component: DMD
          Assignee: nobody at puremagic.com
          Reporter: atila.neves at gmail.com

D:
     extern(C++) interface DClass { int getIndex() const; }
     extern(C++) void useObj(in DClass dclass); //I also tried const DClass

C++:

     struct DClass { virtual int getIndex() const = 0; }
     void useObj(const DClass* dclass); //DClass* works though!

The code above refuses to link. Whether not the D declaration for useObj is
marked `const`, or `in` makes no difference, either way the C++ declaration
can't have const in it.

OTOH, if instead it's `ref const(DStruct)` and `const DStruct&` (or the
equivalent pointer declarations it links fine.

I'm aware of the differences between const in C++ and D, but the above makes it
worse: D can happily think it's const while the C++ code is free to do whatever
it wants without even having to use const_cast.

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