D arithmetic problem

[Don]

Steven Schveighoffer wrote:
> On Thu, 04 Jun 2009 02:00:27 -0400, Don <nospam at nospam.com> wrote:
> 
>> bearophile wrote:
>>> Denis Koroskin:
>>>> Shouldn't bitwise operations be disallowed on signed types at all?
>>>  It sounds OK to me, do Don & Walter agree?
>>
>> Hmm. If you are doing bitwise operations, you are treating the number 
>> as unsigned, no doubt about it. Some observations:
>>
>> * The use of -1 for "all bits set" is in widespread use and is important.
>>
>> ushort x ^= -1;
>> uint y ^= -1;
>> ulong z ^= -1;
>> probably needs to remain valid.
>> But then consider
>>   (x ^ -1) + y
>>
>> What is the type of x^-1 ? Is it ushort? Or int?
>>
>> * A lot of existing C code uses bitwise operations on ints.
>> * size_t had better be unsigned!
> 
> Easy:
> 
> ~0.  It's not even extra characters :)  I'd say I use that way more than 
> -1 (which is probably never).
> 
> That being said, I readily type int WAY more than uint when keeping 
> track of any integral type, including using bitmasks.  If I don't ever 
> use the sign bit in my bitmask, it doesn't matter.
> 
> Also, think about porting code from Java which has no unsigned types.  
> You don't want to have to sit and think about what each variable really 
> means (should it be converted to uint?).
> 
> So I think logic operations on signed types should be allowed, but being 
> able to use -1 as "all bits set" isn't a good argument for it. 

Yes. The Java argument is a stronger one. (Anyway, you could treat the 
literal -1 as a special case).

  I'd much
> rather see an error for the uncommon widening operations without an 
> explicit cast.

Agreed, I think that's the only case that's a problem.