Mixed int/BigInt foreach interval

[Timon Gehr]

On 09/26/2011 11:05 PM, Jonathan M Davis wrote:
> On Monday, September 26, 2011 13:47 Paul D. Anderson wrote:
>> bearophile Wrote:
>>> Time ago I've asked to use BigInt with iota too (no D changes needed
>>> here): http://d.puremagic.com/issues/show_bug.cgi?id=6447
>>
>>> because currently this doesn't work (std.traits.isIntegral needs to
> change, and there changes needed in iota too, because it can't use the current
> std.traits.unsigned, because a BigInt has no ".min" field):
>> Yes, it would be nice to allow isIntegral, isArithmetic, etc. to recognize
>> library types and not just built-in types.
>>
>> This would be helpful for, for instance, rational numbers and decimal
>> numbers (BigDecimal and decimal32, decimal64, decimal128.
>>
>> As an aside, for those who are interested, the Decimal library implementing
>> the numbers listed above is very near completion. Just some testing and
>> tidying to do before it can go on the review queue.
>
> I think that we need to be _very_ careful about the implications of making
> isIntegral and other similar traits functions work with non-primitive types.
> There could _easily_ be code which assumes that it's going to get primitive
> types when isIntegral is true. Take the integer swapping code in std.bitmanip.
> It would fail miserably if all of a sudden BigInt worked with isIntegral, and
> you tried to use BigInt with it.
>
> I can see we might want to have isIntegral work with BigInt, but I do _not_
> think it's necessarily the case that it's actually a good idea. We need to be
> careful about the implications of all of that and make very informed decisions
> about the changes that we make to std.traits, or a lot of code is going to
> break in non-obvious ways.
>
> - Jonathan M Davis

The issue is that isIntegral does not actually check if the data type 
represents integers, it checks if the type is some sort of bit vector 
with two's complement arithmetics defined on it.

Therefore, BigInt should never be included into isIntegral. But I 
totally agree with bearophile that some solution has to be found to make 
BigInt work with generic functions in Phobos.