Re: A case where Ada defaults to unsafe?

[Ted Dennison<dennison@telepath.com>]

In article <3C34E43E.5070906@mail.com>, Hyman Rosen says...
>
>Ted Dennison wrote:
>
>> In article <3C34D252.4070307@mail.com>, Hyman Rosen says...
>> 
>>>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"?
>>>
>> 
>> Perhaps for ex-C programmers it is. But that's certianly not the only pitfall in
>> the language for ex-C programmers.
>> 
>> If you were instead brought up to believe that boolean "and" is communitive,
>> like they teach in math/logic classes, then it makes perfect sense. In that
>> case, "and then" is just a nice shorthand for " then if ... then".
>
>
>You haven't answered my question, though. Isn't the commutative semantic
>less safe than the short circuit one?

Yes I have, but I'll do it again: Its only less safe if you are an ex-C
programmer that expects the world to look like C. 

Let's analyze this a little deeper, shall we? Under what conditions is this
unsafe?

The typical use of "and" and "or" is to perform clasical boolean math, and
perhaps to do different things based on the result. Which is more "unsafe" in
this typcial circumstance? Neither really. 

What you are talking about is a different situation where you may realise that
something like dereferencing a pointer will cause problems when the pointer is
null. So you tell yourself, "self, I'd better prevent an error by first putting
in a check to see if the pointer is invalid, then not performing that second
operation if that's the case". So you consciously put in the check. 

So here we are, consciously adding code to implement a "don't do this check
unless this other check works out" operation. The only way to screw this up is
to use the wrong language features, and the only way we are ever going to do
that would be if somewhere along the line something (eg: C) convinced us that
these two quite different types of operations are actually the same.

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T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

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