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From: dewar@gnat.com (Robert Dewar)
Newsgroups: comp.lang.ada
Subject: Re: System.Address'Size - not a static integer expression?
Date: 19 Apr 2002 19:26:50 -0700
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Wes Groleau <wesgroleau@despammed.com> wrote in message news:<3CC03241.883A6E33@despammed.com>...

> Now that is entirely possible.  They are not opposites
> in the RM, but they are opposites in general use.

Yes, but this general use is fuzzy, since as I pointed out
before, the notion of "known-at-compile-time" is recursively
undecidable. Furthermore, I am not aware of the
specific term static having been used in the context of
any previous language.

It's unusual for a language to give semantic significance
to this notion. In most languages, the compiler is free
to evaluate or not evaluate any expression at compile time
as it pleases.

This is also true in Ada, but a recognized *subset* of
compile time evaluable cases is identified as part of the
language. This allows many things to be checked at compile
time (e.g. completeness of case statements) without having
to limit the case tags to literal constants.

Inevitably, the class of static expressions identified in
the RM *must* be a subset of the expressions that can be
evaluated at compile time. This is not a recognition of
practical necessity, it is a mathematical theorem that can
easily be proved by analogy to the halting problem.

Of course a good Ada compiler will go well beyond this minimal subset
and evaluate many more expressions at compile time, but it is *NOT*
allowed to consider these
to be static in the formal sense.