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From: n_brunot@my-deja.com
Newsgroups: comp.lang.ada
Subject: Re: Ok sorry, it is just a book gives no feedback.
Date: Thu, 04 Jan 2001 15:49:58 GMT
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In article <931t08$5u5$1@nnrp1.deja.com>,
  Robert Dewar <robert_dewar@my-deja.com> wrote:
> In article <931r2l$4ai5t$2@ID-25716.news.dfncis.de>,
>   "Nick Roberts" <nickroberts@callnetuk.com> wrote:
>
> > My own opinion is that, generally, functions should have no
> > side effects
>
> This principle is in general a reasonable one, but it is not
> easy to define what this means. Nick goes on to give an
> explanation, but his explanation is wrong, it would forbid
> many functions, e.g. anything that allocates and returns a
> pointer, which is far too severe.
>

Well "generally" seems reasonable and never said that this behavior is
forbidden.
Of course some functions must have side effects, but I agree it's better
to avoid it each time side effects are not necessary.

Just look the following code (simplified from old buggy code).
Depending if the compiler evaluate right or left term first for "&",
you get quite different behavior ....
This is a pathologic case, but good example to show why it's not so bad
to avoid side effect each time you can, and keep constantly testing your
code on different Ada compilers ...

with Text_Io;
procedure Test is
   N : Natural := 10;
   function Decrement return String is
   begin
      N := N - 1;
      return "A";
   end;
   function Recursive return String is
   begin
      if N /= 0 then
         return Decrement & Recursive;
      else
         return "A";
      end if;
   end;
begin
   Text_Io.Put_Line (Recursive);
end;


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