Signed word lengths and indexes

[Don]

KennyTM~ wrote:
> On Jun 17, 10 21:04, Don wrote:
>> KennyTM~ wrote:
>>> On Jun 17, 10 18:59, Don wrote:
>>>> Kagamin wrote:
>>>>> Don Wrote:
>>>>>
>>>>>> (D has introduced ANOTHER instance of this with the ridiculous >>>
>>>>>> operator.
>>>>>> byte b = -1;
>>>>>> byte c = b >>> 1;
>>>>>> Guess what c is!
>>>>>> )
>>>>>
>>>>> :)
>>>>> Well, there was issue. Wasn't it fixed?
>>>>
>>>> No. It's a design flaw, not a bug. I think it could only be fixed by
>>>> disallowing that code, or creating a special rule to make that code do
>>>> what you expect. A better solution would be to drop >>>.
>>>>
>>>
>>> I disagree. The flaw is whether x should be promoted to
>>> CommonType!(typeof(x), int), given that the range of typeof(x >>> y)
>>> should never exceed the range of typeof(x), no matter what value y is.
>>
>> The range of typeof(x & y) can never exceed the range of typeof(x), no
>> matter what value y is. Yet (byte & int) is promoted to int.
> 
> That's arguable. But (byte & int -> int) is meaningful because (&) is 
> some what "symmetric" compared to (>>>).

See below. It's what C does that matters.

>> Actually, what happens to x>>>y if y is negative?
>>
> 
> x.d(6): Error: shift by -1 is outside the range 0..32

If y is a variable, it actually performs   x >>> (y&31);
So it actually makes no sense for it to cast everything to int.

>> The current rule is:
>> x OP y means
>> cast(CommonType!(x,y))x OP cast(CommonType!(x,y))y
>>
>> for any binary operation OP.
>> How can we fix >>> without adding an extra rule?
> 
> There's already an extra rule for >>>.
> 
>     ubyte a = 1;
>     writeln(typeof(a >>> a).stringof);
>     // prints "int".
> 
> Similarly, (^^), (==), etc do not obey this "rule".

The logical operators aren't relevant. They all return bool.
^^ obeys the rule: typeof(a^^b) is typeof(a*b), in all cases.

> IMO, for ShiftExpression ((>>), (<<), (>>>)) the return type should be 
> typeof(lhs).

I agree that would be better, but it would be a silent change from the C 
behaviour. So it's not possible.