Re: glossary for egcs - request for contributions

[Marc Espie <espie at quatramaran dot ens dot fr>]

In article <199904280705.AAA04952@atrus.synopsys.com> you write:
>> > As I quite possibly will miss some terms as they're too familiar to me, I'd
>> > like to ask that anybody who thinks he has (or had) problems with the terms
>> > used in egcs (both messages and documentation) send me these terms for
>> > inclusion.
>> 
>> For C++, 'covariant return types', and 'contravariance violation' are
>> probably most frequently confusing.

>I can't think of any explanation for these errors that doesn't require at
>least a paragraph.  Maybe we should add a URL or reference to a node in
>gcc.info, or both, to the error message, since it seems that when people
>encounter them they immediately post to gnu.g++.help or egcs.

Is there any online paper that clearly explains, in understandable words,
what covariant/contravariant means in an object type theory ?

I have read several books on the subject, but I wouldn't recommend them to
someone who would just like to know what's going on.

On the other hand, I believe that, to understand what these error messages
means, one usually has to have at least an intuitive grasp of what these
concepts are... without a conceptual model, one is going to lose, sooner or
later.  Getting past the compiler,  but writing hierarchies in which lists of
triangles inherit from lists of shapes, or some other classical mistake.

What I mean is, if we want to put an explanation for that one in, it had
better cover the problem fairly, not give the casual reader a superficial
understanding of what's going on.