Re: Ada 200X

["Robert I. Eachus" <rieachus@attbi.com>]

Vinzent Hoefler wrote:

> Because the view conversion to a grandparent is of course allowed,
> this is little tricky if not to say error prone sometime.
> 
> Well, yes, I know, you should always design your object hierarchy
> beforehand. ;-)

In one sense this is a valid criticism of the "Ada way" of doing things. 
  In another it is totally bogus.

Ada tagged type derivation trees tend to come in two flavors.  The first 
is one parent with a lot of children. (A bush.)  The class rooted at 
Controlled is like this.

The other common type of Ada derivation tree is a pole.  You have a 
sequence of generic instantiations in the private part of a package 
declaration, each instantiation creating a new mixin.  In the body of 
the package you have lots of view conversions.  But the view conversions 
are definitely not to parents or grandparents, they are to specific 
mixins.  Any added mixins should not change any of the current uplevel 
references.

So I have done lots of changes to type hierarchies in Ada, and I don't 
think I have ever needed to change a view conversion unless I have done 
the gun, foot, shoot, optimization.  (If you really, really need to 
change the name of an instantatiation, you have to be ready to do a 
global search and replace against the body and all child packages.  The 
problem is if you used a name originally that matches some component 
name or the like...)