Re: Equality operator overloading in ADA 83

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

Bob Duff said

<<Robert, I think you misunderstand his point.  I think he's saying that
if so-and-so is implementation dependent, the RM should say, "so-and-so
is implementation dependent", rather than being silent on the issue.  I
agree with that.  Otherwise, you're never quite sure whether the
language designers meant it to be undefined, versus they never thought
about it.  In this particular case, I think the language designers never
thought about whether "=" should compose for various predefined types,
such as Bounded_String, so its implementation-dependence is accidental.

In general, this principle is good, and I tried to obey it in RM95 -- if
something is undefined, then the RM should say so explicitly.  Nothing
should be undefined just because the RM doesn't bother to define it.

Anyway, this is why we have an AI on this point.>>


I do not disagree that it is a good idea to pin down this particular
lack of specification, but I strongly disagree with the general principle
here. The idea of a package spec in Ada 83 or Ada 95 is that you are
free to implement the body anyway you like, and of course there are things
that are left open. FOr example, the paragraph above would require us to
say things like:

a) it is implementation defined what the value of x'size is for the following
types (Address, Unbounded_String, ...)

b) It is implementation defined whether it is possible to apply pragma Pack
to arrays of types ....

c) It is implementation defined what values of component size are permitted
for arrays of types ...

etc.

If you think these all need to be made explicit, get busy, you have a lot
of AI's to write!