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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: Re: += in ada
Date: Tue, 7 Oct 2003 11:56:41 +0000 (UTC)
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Date: 2003-10-07T11:56:41+00:00
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* Dmytry Lavrov wrote:
> begin
> declare_new_name a _for_ X(b(i).all+7);
> -- for example, "a is X(b(i).all+7)"
> a:=a+2/a;
> end;

declare
   a : Typ renames X(b(i).all + 7);
begin
   a := a + 2/a;
end;   

is legal Ada and a common idiom.

> "+=" is a idea about in-place operations,and @ is about readability.

Both ideas fail on considering a consitent semantic for volatile types and
exception handling. In both cases it's necessary to require a temporary copy
of the LHS. So nothing is gained from this proposal, beside a clear semantic
about access frequency for volatile data (one read and one write access).

So I have to conlude, that the whole "idem" Idiom is useless at all.

In order to generate a more general solution, the S'Type attibute would
helpful, because it's possible to write:

declare
   a : a'Type renames X(b(i).all + 7);
begin
   a := a + 2/a;
end;   

> IMO,in place operations should be used as normal procedures like
> inc(a,b) or juliafractalstep(z,c);

Yep.