Re: Inheritance versus Generics

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Craig Smith asks

<<Generics were a very power feature of Ada-83.  With the OO features
introduced into Ada-95 (in particuliar, the tagged record and ability to
inherit), are Generics obsolute?  I would guess since several features
were added to generics (like generic formal package parameters), the
answer is no.  Does anyone have any thoughts on this?>>

One group that has thoughts on this is the C++ design committee. Originally
the attempt was to develop OO stuff, and decide that genericity was not
needed, but eventually it was clear that this was over-restrictive, and
so genericity (templates) was added.

Note that the Ada 83 design is an interesting dual. The Ada 83 design
committee was well aware of the object oriented approach (many of them
had been using Simula-67 for over a decade -- it is well to remember
that the basic OO idea are ancient). Their experience said that writing
large scale programs using the OO approach was ineffective, and they
very conciously decided against incorporating such features into Ada 83,
deciding that the same basic functionality could be achieved in a language
that concentrated on providing powerful genericty.

Now at least in some sense, Ada 95, shows the same phenomenon as C++,
in deciding that both are necessary. However, the situation in the Ada 95
case is a little more clouded, since the basic motivation for adding OO
stuff was not purely technial, but the decision was largely driven by
"following the trend" fadism. Only time will tell the full story here ...

A lot of people find genericity to be much more significant than OO stuff
(a good example of this is the designers of the standard template library
in C++, which uses genericity extnsively, but inheritance barely at all.