Re: A case where Ada defaults to unsafe?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Brian Rogoff <bpr@bpr.best.vwh.net> writes:

> On Fri, 4 Jan 2002, Robert A Duff wrote:
> > If you're looking for cases where Ada makes the default less safe, I can
> > think of a few.  Here's one: "X: T := ...;" is a variable, whereas
> > "X: constant T := ...;" is a constant.  IMHO, it should be the other way
> > around ("X: var T := ...;" for a variable), since constants are safer
> > than variables.
> 
> I know I'm digressing a bit, but I'd prefer that ":=" not be used for
> declaring the value of a constant, since I think of that as being
> different from assignment.

It seems to me that initializing an object is conceptually different
from an assignment statement, and therefore deserves a different
notation.  But I would use the same notation for initializing both
constants and variables.  I'm not sure I like "=", because we already
use that for equality tests.  How about ":=" for init, and ":==" for
assignment statements?  (Imagine you're designing a language from
scratch, here.)

>... Better to use "=" IMO. Of course I am now
> spoiled by functional (quasifunctional :) languages like ML where
> assignment is far less frequent than in Ada or C++. Assignment and
> equality hide a lot of complexity behind a simple facade; that seems to
> have been recognized by the Ada designers.

A related issue is limited types: you ought to be able to return a
nonlocal object from a function, you ought to be able to use aggregates,
and you ought to be able to do initialization.  It's really the "fetch
value out of object" operation that should be considered naughty for
limited types.  Not the assignment operation.

- Bob