[petsc-dev] declaring argument as const basic type in PETSc

[Jed Brown]

On Wed, Aug 17, 2011 at 19:33, Mark F. Adams <mark.adams at columbia.edu>wrote:

> I know C++ does not have an interface-class like some languages, but you
> can get what you want with coding policy, eg, have base classes with all
> virtual functions (and no data of course).  So there is no explicit language
> support; a flaw yes, but fatal?  Petsc relies on policy a lot - as this
> discussion thread amply shows.


That doesn't work because adding a new (private even) virtual method changes
the ABI. To get an decent encapsulation and ABI stability with C++, you have
to make an end-run around the type system and have a base class with zero
virtual functions and zero private members. You forward-declare an private
object here:

class TheThing_Private;

and all the virtual functions go inside of that thing. This is basically the
object model in PETSc, but you get to call methods object.Method(args)
instead of ClassMethod(object,args).
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