RTTI portability

[Martin von Loewis]

> I don't know.  Most of this thread arose because someone wanted the
> RTTI member names to be normative, which only matters if they are to be
> referenced outside the implementation's runtime library, i.e. by users.
> Whoever it was, though, hasn't been standing up with examples.  Perhaps
> that's not a real issue.

To access the fields of typeinfo objects, you don't have to derive
from those objects. Instead, you can do

  type_info &foo = static_cast<class_type_info&>(typeid(bar));
  cout<< foo.base_type->name() << endl; // prints name of base class

There may be applications of browsing through the base class list of
an object: if you want to efficiently classify an object into a number
of root classes, that approach may be faster than a series of
dynamic_casts.

However, I can't foresee an application where the user would need to
inherit from the RTTI classes.

> Again, my terminology at fault.  But the compiler will have problems.
> Whether it uses its (different abi.h) or its different internal
> assumptions about it, the difference could create problems.

Only if the number or order of fields is different. If it has
different virtual functions in the header file, it won't be a problem:
the compiler only emits a reference to the vtable, not the vtable
itself - that one is in libcxa.so. Since the compiler will also need
to use the ABI routines for processing typeinfo objects from
libcxa.so, there will be no problem.

Regards,
Martin