Re: proposal for new assignment operators

[18k11tm001@sneakemail.com (Russ)]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message news:<bdbtav$regf8$1@ID-77047.news.dfncis.de>...
> Russ wrote:
> >     count :+ 1
> >     EulerAngles :* D2R

> The real problem is not to find a better sequence of characters. The real 
> problems are:

Agreeing on a sequence of characters is not a *technical* problem, but
it is a problem nevertheless, and it could actually turn out to be
very difficult

> 1. Ada does not have any assignment operator. It has an assignment 
> statement. Carefully observe all the consequences of that. When I and 
> others proposed to allow operators be implemented by procedures, the goal 
> was to approach this problem.

As someone pointed out on an earlier thread, "+=", ":+", or whatever
you call it, is just "semantic sugar" for a procedure like
"Add_Matrix". It really has nothing to do with assignment per se. So I
fail to see the relevance of the fact that Ada has no assignment
operator.

> 2. Ada isn't C++. One have to provide an easy and safe way to ensure that 
> "+" and in-place-"+" have compatible semantics. The language default has to 
> be safe. This is why I made another proposal to invent a mechanism 
> instructing the compiler to deduce one operations from others. Such things 
> exist presently for "/=" which is automatically deduced from "=". And for 
> ":=", which is automatically deduced from Finalize, Adjust and assignments 
> of the components. IMO we need something like:

I agree it would be nice to have language enforcement of consistency
between operators, but I think that would be going beyond what Ada
already allows. Does Ada require a user-defined "+" operator to be
consistent with the corresponding "-" operator? No. "+" could add
matrices, and "-" could send email to Santa Claus.

> procedure ":+" (L : in out Matrix; R : Matrix);
> function "+" (L, R : Matrix) return Matrix;
> for "+" use ":+";

How about

function "+" (L, R : Matrix) return Matrix is
    Result: Matrix := L;
    begin
    Result :+ R;
    return Result;
    end "+";

> But it is not an easy issue. Consider tagged types. You have overridden 
> ":+", but not "+". What have the language to say in such cases? Again, Ada 
> need not to become Ada += C++; One C++ is already too much for our planet.

Maybe I'm missing something, but I don't see why these concerns are
any different than they would be for any other function or procedure.

> -------
> Provided 1.& 2. one could just enlarge the set of lexical elements and let 
> the programmer to choose what he/she wants. I would like to see "<+>", 
> "[+]", "(+)", "+:=", "<+>:=" etc added, but is that worth the efforts?