Re: virtual operator +

From:

Hunk <santosh.udyavara@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 11 Sep 2007 11:31:24 -0700

Message-ID:

<1189535484.955065.160880@22g2000hsm.googlegroups.com>

On Sep 11, 11:09 pm, "Maarten Kronenburg" <M.Kronenb...@inter.nl.net>
wrote:

In addition to my previous reply I have to be a bit more precise. In my
integer class the operator+ returns a base object, which can then be
converted back to a derived object by operator=. This is to make equivalent
arithmetic expressions have equivalent results. But this can only be done if
the derived class has no extra data members (in addition to the data members
of the base class), otherwise they would be sliced off. Now when your
derived class would have extra derived data members, this slicing problem
makes things more complicated. In that case you would need also a derived
operator+ which returns a derived object. This would save your derived data
members, but then equivalent arithmetic expressions with both base and
derived objects may lead to unequivalent results. You would have to work
this out for a few used arithmetic expressions to see if that would happen.
Regards, Maarten.

Bull's eye... my base class has no data members and derived class have
all the members
the design is like
class Base_string{};

template<size>
Class Char_string:Base_string
{ char d_the_string[size];
                   size_t d_size;
                  };
template<size>
Class Hash_string:Base_string
{ char d_the_string[size];
  size_t d_size;
  int d_hash; };

so here i'm stuck while overriding the virtual operator+ in the
Base_string as it would mess up what it is pointing to (eg in the
earlier post)