Re: proposal for new assignment operators

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

Russ wrote:

> As most of you are aware, several very popular programming languages,
> such as C, C++, Java, Perl, and Python, have what are called
> "assignment operators." The most important of these operators are
> "+=", "-=", "*=", and "/=".
> 
> On a recent thread, the usefulness of those operators was discussed in
> detail, so I won't rehash it.
> 
> One of the problems with adding these operators to Ada is that "/=" is
> already used for "not equals." So I suggested that the Ada version of
> these operators could be ":+", ":-", ":*", and ":/". I did not get
> much of a reply, but I think it's an idea worth considering, so I am
> repeating it here.
> 
> These operators would be consistent with the ":=" assignment operator
> of Ada, and I don't think they conflict with any established Ada
> operator. I actually think they make *more* sense than the usual "+="
> type operators. Consider, for example,
> 
>     count :+ 1
>     EulerAngles :* D2R
> 
> I'm wearing my asbestos underwear, so have at it!

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

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.

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:

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

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.

-------
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?

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de