Is -1 > 7 ?

[Andre Artus]

On Sunday, 11 August 2013 at 17:01:46 UTC, Yota wrote:
> On Friday, 9 August 2013 at 17:35:18 UTC, monarch_dodra wrote:
>> On Friday, 9 August 2013 at 15:28:10 UTC, Manfred Nowak wrote:
>>> michaelc37 wrote:
>>>> WTF -> -1 is greater than 7 ????
>>> 
>>> From the docs:
>>>
>>> It is an error to have one operand be signed and the other 
>>> unsigned for a
>>> <, <=, > or >= expression.
>>>
>>> -manfred
>>
>> Interesting. I didn't know it was documented as being an 
>> outright error, I thought it was just "surprising"...
>>
>> I don't think Walter will ever accept to make it illegal 
>> though, breaks too much code. If this was a change he was OK 
>> with, I think we would have had it since day one, or at least, 
>> years ago.
>
> I remember hearing somewhere that D is about enforcing users to 
> write CORRECT code.  I would really be disappointed with the 
> language if this sort of gotcha weren't eliminated.
>
> If I look at this assert, I shouldn't be expecting it to pass.
> static assert(-1 > cast(size_t)7);
>
> IMHO, as long as this sort of comparison causes a compile-time 
> error, as the docs say they should, this kind of breaking 
> change is the of very good sort.  The sort that reveals bugs in 
> code. (Like when they changed the NULL macro to mean 'nullptr' 
> instead of 0 in C++.) I couldn't imagine a programmer 
> exploiting this intentionally, as it serves no purpose.

I agree, breaking changes that expose bugs in your code are the 
good kind. The time spent fixing compile time errors is more than 
compensated for by the time saved not having to hunt down those 
bugs.

Having worked with languages where reference types are 
non-nullable by default I wish more languages did the same. More 
often than not when a null makes it past the public interface to 
an app or library then it is an error. So much code can be 
simplified when the compiler looks a Null square in the mug and 
declares, "thou shalt not pass!"

I dislike implicit conversions at the best of times, but implicit 
conversions that change sign or drop bits is a design mistake 
that needs to be fixed. I break out in convulsions at the sight 
of them.

D has many great features [1] that help eliminate common errors, 
but there still seems to be a few rough edges.

1.I recently learned about D's ability to write integers with 
underscores, this is a great feature (if a bit tricky to generate 
a lexer for [without handwritten code]).
I think that,
0b0010_1001__1101_1001__1101_1100__1101_100
is so much easier to grok, and to see a that a digit may be 
missing from the end, effectively a right shift, than the 
alternative
0b0010100111011001110111001101100

Only trip up is that 0b__1 == 0b1__ == 0b_1_ == 1 (for 
understandable reasons, but something to keep an eye out for)


>
>> Related: std.algorithm.max *is* sign aware, and you can use 
>> code such as:
>> if (a == max(a, b))
>>
>> I have an pull request which creates the premise of functional 
>> "less"/"greater" operators, which are also sign aware:
>> https://github.com/D-Programming-Language/phobos/pull/1365/files
>>
>> *If* it goes through, and *if* we make them public in 
>> std.functional, then it allows code such as:
>> int a = -1;
>> size_t b = 7;
>> assert(a.less(b)); //Passes
>
> That is pretty cool, but unless the comparison operators 
> actually use that code, (which they probably won't, since it's 
> not a library thing?) it will only provide a workaround to the 
> problem.