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From: dmytrylavrov@fsmail.net (Dmytry Lavrov)
Newsgroups: comp.lang.ada
Subject: Re: += in ada
Date: 13 Oct 2003 01:32:37 -0700
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"Robert I. Eachus" <rieachus@comcast.net> wrote in message 
....
to save or not to save.
....

Here
a:=a+b;
('a+=b')

,value of a should not be corrupted,because it may be needed to find
what to do  in case of exception!
in a:=a+b it's simple to recover old value of a,but
a:=a*b;  here it's not so simple.

Of course in your example are no difference:
a:=b*c;
here we ready to lost value of a and don't use a in expression,and
normally(not in speculative examples) don't need to use a in case of
exception.If we have exception handling for expression,normally this
exception handler is a logically "part of expression",and normally may
use all values from right side of :=,to find value for left side.
 
> with Text_IO; use Text_IO;
> with Integer_Text_IO; use Integer_Text_IO;
> procedure Issue is
>    X,Y,Z: Integer := 0;
> begin
>    Get(X); Get(Y);
>    if X * Y > Integer'Last
>    then
>      Put_Line("Overflow!");
>    else
>      Z := X * Y;
>      Put_Line("Okay");
>    end if;
> exception when Constraint_Error =>
>    Put("Exception Raised. Z = ");
>    Put(Z);
>    New_Line;
> end Issue;
What,there are exception in X * Y > Integer'Last 
if there are overflow on X*Y?
And if so,how Put_Line("Overflow!"); could work?

(yes ,i'm is a newbie to ada)