Re: A case where Ada defaults to unsafe?

[dewar@gnat.com (Robert Dewar)]

Hyman Rosen <hyrosen@mail.com> wrote in message news:<3C34D252.4070307@mail.com>...
> Frank J. Lhota wrote:
> 
> > The situation is quite similar in C/C++; if you use the siumpler & and |
> > operators, they do not short-circuit. In either C/C++ or Ada, experienced
> > programmers know what needs to be done in order to get short-circuiting.
> 
> 
> In C/C++ "everyone" knows that & and | are for bit twiddling and && and ||
> are for combining logical expressions.

Well any vaguely competent Ada programmer should equally
well know that in Ada "and then" and "or else" short circuit and "and"
and "or" do not.

If you think, as apparently you think C programmers think,
that all combination of logical expressions should be done
using the more verbose operator (about twice as long in
both C and Ada) then always use "and then" and "or else".
This is more or less the philosophy in GNAT (the one exception is when
logical variables are combined, and
indeed in C it is reasonable if Is_Undefined and Is_Unsafe
are booleans to say

   if (Is_Undesigned | Is_Unsafe) then

Indeed with some not very clever C compilers, the above
will give significantly better code than using || :-)

> But get away from C/C++ for a moment. In pure Ada terms, isn't it less safe
> for the defaults to be "and" and "or" instead of "and then" and "or else"?

Defaults? What are you talking about? There are two operators, one is
called AND and one is called AND THEN,
and neither is chosen by default, you use the one you
want.

Exactly the same as in C, where you use either & or &&.
You claim that the difference is that in C everyone knows
which to use, and think that this is not the case in Ada,
but is it not the case that you are simply saying you are
more familiar with C than with Ada? Which may of course be
true, but does not lead to an even playing field analysis.

This is in fact a place where C and Ada take a very similar
approach, both providing a more verbose operator for the
short circuiting case. As in C, the AND in Ada can also
mean bit wise AND (like &) as well as being used for
combining boolean values.

I do think there is an argument for making AND mean short
circuiting, and having a separate operator for bit-wise
AND. I would apply the same argument to C, and say that it
would have been better if the normally used and/or were
spelled & | instead of the awkward && and ||

(yes, I know, && and || seem "perfectly natural" since you
have used them so long, sort of like English spelling seems
logical to those who have had to deal with it for ever :-)