Re: A situation where private inheritance is useful
Juha Nieminen wrote:
Let me share with you a realization I had about private inheritance.
As we all know, C++ supports three types of inheritance: Public,
private and protected. From these only the public inheritance is a
"true" inheritance from an object-oriented point of view. If you inherit
privately, there is no "is-a" relationship between the derived and the
base classes, and thus private inheritance does not conform to
object-oriented design. So why have this odd private inheritance at all?
[...]
As soon as one realizes that inheritance is just what it is, and any
access specifier simply limits the area where the relationship between
the derived class and the base class is, well, *accessible*, then
everything with protected inheritance (and private inheritance as well)
becomes kind of clear. I probably wouldn't call it an epiphany, but...
So, the "is-a" relationship *does in fact exist* in all three cases,
only it's "known" /to everybody/ in case of the public inheritance,
/only to descendants, members, and friends/ in case of protected one,
and /only to friends and members/ of the derived class in case of
private inheritance.
Simple as that.
Please don't get me wrong, in no way I am trying to contradict your
findings, except for one statement in the quoted paragraph: 'If you
inherit privately, there is no "is-a" relationship between the derived
and the base classes'.
V
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