Re: S-expression I/O in Ada

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Wed, 18 Aug 2010 14:02:48 +0200, Natasha Kerensikova  
<lithiumcat@gmail.com> a écrit:
> I thought discriminant really was like C's union, allocating enough room
> for any possible sub-object to fit (and adding an overhead to explicit
> which sub-object is currently used, to prevent C union's unfamous
> undefined behaviour issues). Actually it's much more than a union.

Another point to tell you (if ever you like this new point) : you may  
think of it a what is also named “Tagged Union”, but while Tagged has a  
more particular meaning in Ada, better not to confuse with this and use  
the expression “Disjoint Union” instead.

Do not really like WikiPedia, but some time I do not have any other source  
to suggest to read:
http://en.wikipedia.org/wiki/Disjoint_union

And to be complete, about Tagged Union also (not to be confused with Ada  
tagged type, while these are similar in some ways):
http://en.wikipedia.org/wiki/Tagged_union

You may also think that the discriminant is part of the object value,  
which a main topic and is something C strictly do not know about (well,  
Ada also have unchecked union, but pretty sure you do not need it here...  
this is to be used in interfacing with the outside world only).