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.
