Signed-unsigned comparisons in Phobos

[Marco Leise]

Am 12.08.2011, 17:48 Uhr, schrieb Simen Kjaeraas <simen.kjaras at gmail.com>:

> On Fri, 12 Aug 2011 14:55:26 +0200, Marco Leise <Marco.Leise at gmx.de>  
> wrote:
>
>> Am 12.08.2011, 12:22 Uhr, schrieb kennytm <kennytm at gmail.com>:
>>
>>> Don <nospam at nospam.com> wrote:
>>>
>>>> I've had a look at a dozen or so of these, and they were all real. I
>>>> didn't see any which require a cast to "make the compiler shut up".
>>>> That's pretty impressive. In C++ I find that such messages are nearly
>>>> always false positives.
>>>>
>>>> The one case where it's a bit annoying is this:
>>>>
>>>> int [] x = new int[6]; // or x = some array literal.
>>>> for (int i = 0; i < x.length; ++i) {...}
>>>>
>>>> Here is a suggestion for how we could eliminate such false positives.
>>>> http://d.puremagic.com/issues/show_bug.cgi?id=6478
>>>
>>> Doesn't this require flow analysis? And the type of index 'i' should be
>>> 'size_t' anyway.
>>
>> I think I once shot myself in the foot with this when I used 'auto' for  
>> 'i' and the code wouldn't compile on x86_64, because I assigned the  
>> variable to an int or uint later on in the loop. You just have to be  
>> aware that this is an unsigned integer of machine word length. So I  
>> agree with kennytm on this.
>>
>> Just remember that reverse loops are written like this:
>>
>> for (size_t i = x.length; i-- > 0; ) {...}
>
> I like using the long arrow operator for this:
>    i --> 0 // i goes to 0

This way it is actually fun to cripple the for loop, yay. Still if people  
started to argue that it is a bad idea to modify variables in the  
condition I'd silently agree. So a look at "foreach_reverse (i;  
0..x.length) {...}" might be worth it. I guess after a while I will get  
used to it. It even reminds me of the Pascal "for"-syntax a bit, which is  
"for i := 0 to 9 do ...". It has no receipt for the reverse zero-length  
array loop though as far as I know.