Redefinition of "=", elaboration and learning Ada

[Mats Weber <Mats.Weber@elca-matrix.ch>]

Another reason why I think we should have automatic elaboration order
calculation that works in the simple cases, and no reemergence of
predefined operations once they have been redefined, is that the
majority of Ada programmers do not understand these problems because
they have never studied the language to that level of detail (which is
perfectly OK, one should not be required to read the entire RM three
times to be able to write a piece of software in Ada).

Having to use pragma Elaborate_All when instantiating a generic at the
libarary level is, IMO, counterintuitive and unnecessarilly complicated.

Having predefined "=" reemerge in strange places when it's been
redefined is also counterintuitive, and the text in chapter 12 of the RM
won't help you much if you are not a language lawyer or compiler writer.
And then try explaining to a novice programmer, without making him
believe that the language definition is flawed, that if he makes his
type tagged then everything will work fine :-)

What the user sees when he discovers packages and private types is that
he can define abstractions that he can use without knowing how they are
implemented. What he sees when he discovers a library of generic
components is that he can instantiate them and then use them. In both
cases, he hits what is IMO a severe pitfall: reemergence breaks his
abstraction, and he (potentially) gets Program_Error when he
instantiates his generic.

For me, these are not really severe problems (except that I don't like
the way they were handled in Ada 95) because I know how to fix them. But
how is a beginner going to find his way to tagged types or elaboration
pragmas ? Not very easily I think, unless he reads comp.lang.ada :-)