Matus Chochlik wrote:
On Wed, Oct 21, 2009 at 3:09 PM, Ireneusz Szpilewski <irek@szpilewski.opole.pl> wrote:
Stewart, Robert wrote:
Ireneusz Szpilewski wrote:
[...] I don't care what you call it. There is no good reason to do this in C++.
[snipped examples of using containers of heterogeneous types.]
I'm well aware of uses of this approach and they are usually misguided. A common base class is not terribly helpful. One specific to a particular use case is far more useful. Using your approach encourages programming with dynamic_cast. There are times when it is needed, but its use should be limited and not encouraged generally.
I agree that defining and using a common base class for all other classes in a project is in 99% of cases a very bad idea. There is a book called "C++ Gotchas: Avoiding Common Problems in Coding and Design" and the use of such "cosmic hierarchies" is a gotcha #97 ;-)
Don't look at class hierarchy, look at object. It would be composed of many other subobjects (by means of multiple inheritance), just as a human body is composed of different organs. What's wrong with fact that all men have penises? (I will make "rtti_base" tattoo on mine) Of course man should have one penis, so every class should inherit rtti_base virtually. (By the way, C++ virtual inheritance implementation is broken) I insist on that deriving from rtti_base is voluntary and controlled by a particular class hierarchy designer. In our analogy - every man can have his penis cut off if he (or his wife) doesn't need it. What can you do with penises? We all know what. ;-) And what can we do with rtti_base? If we have pointer to it, we can query the pointed object using RTTI. Ireneusz Szpilewski