automatic int to short conversion - the HELL?

[Ary Borenszweig]

Jarrett Billingsley wrote:
> On Fri, Sep 19, 2008 at 9:45 AM, Ary Borenszweig <ary at esperanto.org.ar> wrote:
>> Jarrett Billingsley wrote:
>>> On Fri, Sep 19, 2008 at 9:29 AM, Ary Borenszweig <ary at esperanto.org.ar>
>>> wrote:
>>>> bearophile wrote:
>>>>> Ary Borenszweig:
>>>>>> No, no. In Java it's an error, an explicit cast is required.
>>>>>> http://www.programmersheaven.com/2/FAQ-JAVA-Type-Conversion-Casting
>>>>>> Which is perfect. It expresses the intents of the programmer:
>>>>> About such matters I suggest you all to also take a look at how Ada
>>>>> works.
>>>>> Ada was designed first of all to create reliable software, so avoiding
>>>>> casting-derived bugs too is essential.
>>>>> D tries to avoid some of the pitfalls of C, to be a language less
>>>>> bug-prone: casts is where D has to improve still in such regards. Time
>>>>> ago
>>>>> (when I was more a D newbie) I have already had a bug in my code because
>>>>> of
>>>>> a casting bug:
>>>>>
>>>>> import std.stdio;
>>>>> void main() {
>>>>>   int n = -5;
>>>>>   int[] a = [1, 2, 3];
>>>>>   writefln(a.length > n); // prints false
>>>>> }
>>>>>
>>>>> A well designed language, even a system language like Ada or D, must
>>>>> avoid
>>>>> such kinds of bugs, regardless the amount of ignorance of the
>>>>> programmer.
>>>> Wow. At first, I thought that was already fixed. Now I've written that
>>>> code,
>>>> compiled it and run it and saw it gives false. Ok, I know a.length is an
>>>> uint because logically it cannot be negative. But... shouldn't it be an
>>>> int
>>>> to avoid this kind of bugs?? You loose nothing doing this. You are never
>>>> going to need an array of 2147483647 positions, much less a bigger array.
>>>>
>>>> I've checked C#, which has uint as a type. The length of an array is an
>>>> int,
>>>> not an unit. A much better choice.
>>> signed-unsigned comparison is, I think, a slightly larger problem than
>>> the type of array.length ;)
>> But if the length of an array is an uint, if you compare it to an int then
>> what bearophile has just shown might happen.
>>
>> Now, if the length of an array is an int, but which is guaranteed to be
>> always positive or zero, then if you compare it to an int or an unit, you
>> always get the desired result.
>>
>> Conclusion: you avoid a bug to happen at zero cost.
>>
>> So... why not?
>>
> 
> The point is that signed-unsigned comparison _in general_ is a bad
> thing, and array.length-int is just one manifestation of it.  If
> signed-unsigned comparison were made illegal, this would be an error.

Now I see what you mean, and I agree.