how to get typeid of extern(C++) classes?

[Steven Schveighoffer]

On 2/15/18 7:42 PM, Timothee Cour wrote:
> is there a way to get typeid of extern(C++) classes (eg for ones in
> dmd/astbase.d but not limited to that) ?
> C++ exposes it via typeid so in theory all the info is there ;
> I would need it at least for debugging (eg if RTTI is not enabled for
> all compilers or in release mode that's fine so long there's a
> documented way to get it for debugging)
> 
> a lot of extern(C++) classes in dmd use hacks like enum values to get
> their type but it's unreliable and doesn't work for all AST classes.
> 
> at least having a way to expose typeid(instance).name() would be a start
> 
> also, that could be used to fix the bug I posted here:
> https://forum.dlang.org/post/mailman.3138.1517949584.9493.digitalmars-d@puremagic.com
> cast overly permissive with extern(C++ ) classes; ( ie that `cast(A)
> b` doesn't care that b is of dynamic type A)
> 

typeid always returns a D TypeInfo object, which is a D-specific animal.

I don't think we can do this for C++ classes.

For D classes in particular, the typeid is a runtime type, gleaned from 
the embedded vtable. For structs, it is a compile-time defined 
reference. Neither of these things would exist for C++ classes.

-Steve