Re: and then... (a curiosity)

[Keith Thompson <kst-u@mib.org>]

stefan-lucks@see-the.signature writes:
[...]
> Well, if the program requirements are that the side effects for A and B 
> actually occur, I consider it poor programming style if people just write
>
>   if A(X) and B(Y) then ... end if;
>
> IMHO, much better style is the following:
>
>   declare
>     Tmp_A: Boolean := A(X);
>     Tmp_B: Boolean := B(X);
>   begin
>     if Tmp_A and Tmp_B then ... end if;
>   end;
>
> This makes the programmers intention clear, "if A(X) and B(X)" doesn't. 
[...]

(As you said in a later followup, you meant B(Y) rather than B(X).)

I disagree.  The shorter form

    if A(X) and B(Y) then ... end if;

makes the programmer's intent absolutely clear to anyone who knows
what "and" means in Ada.  If I saw the other version my first thought
would be to wonder why the programmer didn't just write "if A(X) and
B(Y)".  After a moment's thought, I'd assume that the order of
evaluation of A(X) and B(Y) is significant.  It would never occur to
me that the long form was used to ensure that both A(X) and B(Y) are
evaluated, since the "and" operator already does that.

All programming languages have their quirks, and none of them exactly
follow mathematical notation (in part because there is no single
mathematical notation).  If you try to write code that will be
understandable to someone who doesn't know the language, you'll end up
with an overly verbose mess that can hardly be understood by someone
who *does* know the language.

If I were doing the equivalent of the above in C, whose logical "and"
operator "&&" does do short-circuit evaluation, I probably would
declare the two temporaries.  In Ada, it's just not necessary.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
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