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Date: Tue, 01 Dec 2009 13:13:29 +0100
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: Operation can be dispatching in only one type
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Date: 2009-12-01T13:13:29+01:00
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Robert A Duff schrieb:
> stefan-lucks@see-the.signature writes:
> 
>> On Sun, 22 Nov 2009, Robert A Duff wrote:
>>
>>> Ada uses the term "assignment" to refer to both "initial assignment /
>>> initialization" and "assignment_statement / overwriting".
>>> I'd prefer to use different symbols for the two.
>>> We're not going to change Ada in that regard, for compatibility reasons,
>>> but I'm thinking in my hobby language design to use the term "assignment"
>>> for the initial one, and "reassignment" for the subsequent overwriting
>>> one, and use different symbols for the two.
>>>
>>> So, for a limited type, "assignment" is legal, "reassignment" is not.
>> Distinguishing the two different operations which are written as ":=" in 
>> Ada by using different words and even different symbols would make a lot of 
>> sense. 
> 
> I definitely want to use different symbols as well as different words.

Am I correct in assuming that one important part of this argument
is about referring to the value stored for some variable before
this store has a "reasonable" value? (Where "reasonable" does not
currently have a meaning that can be inferred from the LRM, I guess.)

If so, and presuming the programming language Ada is very much,
and explicitly, about storing and manipulating bits in registers,
memory words, ... of digital computers in a strongly typed fashion:
In this case I would know the use of being carried away by functional,
uhm, phantasm, pardon the expression.  Rather, why not have Ada turn
warnings about "uninitialized" variables into a rule like Java's?

Then we could rely on the language: compilers will detect
uninitialized variables provided these do not have a pragma/keyword/...
to say that uninitialized is what the programmer wants.
Some fancy means to tell the compiler that this variable
does indeed have a good first value like pragma Import.

   X : [constant] Car; -- default init,
                       -- undefined,
                       -- junk bits. Doesn't matter
   --  *no* pragma Import (Ada, X);

begin

   Spare := X.Tire (5); -- would become illegal,
           -- as no value has been assigned yet.
           -- Currently, we get a warning

   if Fast then
      X := Ferrari.Make (...);
   else
      X := Fiat.Make (...);
   end if;

   Spare := X.Tire (5);


Does the phrase "first value" make sense?