Re: Warning
On Mar 4, 8:32 am, Michael Doubez <michael.dou...@free.fr> wrote:
On 3 mar, 21:10, "Alf P. Steinbach" <al...@start.no> wrote:
* Leigh Johnston:
IMHO "don't derive from concrete class" is a poor wording. I prefer
"inherit an interface, not an implementation" (IIRC adapted from
Gamma&GoF).
IMNSHO inheriting from a concrete class is perfectly valid
when you only want to add to the interface of an object -
after all, it is part of the 3 fundamental OOP rules.
Before arguing against the rule, it would be interesting to see
who is proposing it, and why. To date, the only thing I've seen
recently is a mention that Herb Sutter cites it. Until I've
seen why it's being recommended, I can't really argue one way or
the other. (I haven't actuall seen anyone propose it since
about 1995, but I haven't seen everything. Still, I would like
to know what is wrong with something like:
class TemplateBase
{
private:
virtual void customizationFunction();
// with a default implemenation
};
A class using the template method pattern for customization,
but which provides defaults for all of the customization, seems
like a classical example of a case where a concrete class is
actuall designed to be used as a base class (with public
inheritance).
Deriving from classes which weren't designed to be bases (such
as the standard containers) is generally a bad idea. But the
key to whether you should derive from a class or not isn't
whether it is concrete or not; it's whether it was designed to
be used as a base class or not.
--
James Kanze