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From: dewar@cs.nyu.edu (Robert Dewar)
Subject: Re: Uninitialized "out" parameters
Date: 1996/07/21
Message-ID: <dewar.837994885@schonberg>#1/1
X-Deja-AN: 169435894
references: <31EEACDA.64880EEB@sage.inel.gov> <dewar.837740222@schonberg>
 <4sq614$kai@mulga.cs.mu.OZ.AU> <dewar.837899732@schonberg>
 <4stagp$3vg@mulga.cs.mu.OZ.AU>
organization: Courant Institute of Mathematical Sciences
newsgroups: comp.lang.ada
Date: 1996-07-21T00:00:00+00:00
List-Id: <comp.lang.ada>


Fergus said

"Similarly, in a dynamically typed Ada-like language, the code

    procedure x is
        m : integer;
        n : some_other_type;
    begin
       (big chunk of code)
       m := n;
    end;

causes a run-time type error if and only if the big chunk of code halts.
Of course, Ada uses static type checking, rather than dynamic typing;
they report some "spurious" type errors such as for the example above.

There's no reason why Ada compilers couldn't do the analagous sort of
thing for uninitialized variables."

Yes, but Ada is not dyunamically typed, it uses a decidable static type
system, and there are VERY good reasons why comparable static systems
cannot be designed for dealing with the uninitialized variable problem
(please reread carefully my example of the 2 gig array in an allocate
on demand environment -- and response to how your decidable system
would accomodate this requirement).
dp