[swift-users] Range.count can abort
I’m writing some code that deals with ranges of “sequence numbers”, which are consecutively-assigned positive 64-bit integers, thus Range in Swift. I’m having trouble handling half-open ranges with no maximum, which are very commonly used for representing all items created since a certain time. The trouble is, if I represent these with Ranges whose endIndex is UInt64.max, those ranges tend to bomb: let r: Range = 5..___ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
Re: [swift-users] Range.count can abort
> On Apr 16, 2016, at 12:53 PM, Dmitri Gribenko wrote: > > It needs to be a signed integer. And a signed integer needs a distance type > itself. Yeah, there’s an infinite regress implied there, since a distance type has to be one bit larger than its source type. The only plausible solution is bignums. Any talk of adding those to Swift? —Jens___ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
Re: [swift-users] Range.count can abort
On Sat, Apr 16, 2016 at 8:29 AM, wrote:
> Is there any reason that Distance has to be a simple Int? Since it’s defined
> per-type, UInt64 could use a custom struct without impacting the performance
> of other types:
It needs to be a signed integer. And a signed integer needs a
distance type itself.
Dmitri
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Re: [swift-users] Range.count can abort
Is there any reason that Distance has to be a simple Int? Since it’s defined
per-type, UInt64 could use a custom struct without impacting the performance of
other types:
struct UInt64Distance : Comparable { //I'm not sure what else it needs to
conform to
var distance: UInt64
var isPositive: Bool
}
func == (lhs: UInt64Distance, rhs: UInt64Distance) -> Bool {
return lhs.distance == rhs.distance && lhs.isPositive == rhs.isPositive
}
func < (lhs: UInt64Distance, rhs: UInt64Distance) -> Bool {
switch (lhs.isPositive, rhs.isPositive) {
case (false, false): return lhs.distance > rhs.distance
case (false, true ): return true
case (true, false): return false
case (true, true ): return lhs.distance < rhs.distance
}
}
... //The rest of `Comparable`
(I’m assuming it’d need `Comparable`, but a quick glance around with cmd-click
in Xcode didn’t tell me what, if any, protocols `Distance` needs to conform to.)
- Dave Sweeris
> On Apr 15, 2016, at 6:26 PM, Dmitri Gribenko via swift-users
> wrote:
>
> On Fri, Apr 15, 2016 at 4:23 PM, Jens Alfke via swift-users
> wrote:
>> I’m writing some code that deals with ranges of “sequence numbers”, which
>> are consecutively-assigned positive 64-bit integers, thus Range in
>> Swift. I’m having trouble handling half-open ranges with no maximum, which
>> are very commonly used for representing all items created since a certain
>> time.
>>
>> The trouble is, if I represent these with Ranges whose endIndex is
>> UInt64.max, those ranges tend to bomb:
>>
>> let r: Range = 5..> r.count // FATAL ERROR
>>
>>
>> The problem is that Range.count’s type is Element.Distance, and
>> UInt64.Distance is a typealias of … Int. Huh? It’s pretty clear that the
>> distance between two UInt64s can’t be represented by a signed Int64. Why
>> isn’t Distance UInt64?
>
> Hi Jens,
>
> The distance is signed so that we can represent negative distances.
> r.distance(from:to:) should be able to measure distances backwards.
>
> We are aware of this issue, but we don't know of a good solution.
> We'd appreciate your suggestions.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j (j){printf("%d\n",i);}}} /*Dmitri Gribenko */
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Re: [swift-users] Range.count can abort
On Fri, Apr 15, 2016 at 4:41 PM, Jens Alfke wrote:
>
>
> --Jens [via iPhone]
>
>> On Apr 15, 2016, at 4:26 PM, Dmitri Gribenko wrote:
>>
>> The distance is signed so that we can represent negative distances.
>> r.distance(from:to:) should be able to measure distances backwards.
>
> Yeah, makes sense in general, just not for this particular case...
>>
>> We are aware of this issue, but we don't know of a good solution.
>> We'd appreciate your suggestions.
>
> Add Int128! ;-)
>
> Ok, maybe that just pushes the problem further down the road.
Indeed.
> How about making Distance be Double? ;-)
Double only has 53 bits of precision.
Dmitri
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Re: [swift-users] Range.count can abort
--Jens [via iPhone] > On Apr 15, 2016, at 4:26 PM, Dmitri Gribenko wrote: > > The distance is signed so that we can represent negative distances. > r.distance(from:to:) should be able to measure distances backwards. Yeah, makes sense in general, just not for this particular case... > > We are aware of this issue, but we don't know of a good solution. > We'd appreciate your suggestions. Add Int128! ;-) Ok, maybe that just pushes the problem further down the road. How about making Distance be Double? ;-) --Jens ___ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
Re: [swift-users] Range.count can abort
On Fri, Apr 15, 2016 at 4:23 PM, Jens Alfke via swift-users
wrote:
> I’m writing some code that deals with ranges of “sequence numbers”, which
> are consecutively-assigned positive 64-bit integers, thus Range in
> Swift. I’m having trouble handling half-open ranges with no maximum, which
> are very commonly used for representing all items created since a certain
> time.
>
> The trouble is, if I represent these with Ranges whose endIndex is
> UInt64.max, those ranges tend to bomb:
>
> let r: Range = 5.. r.count // FATAL ERROR
>
>
> The problem is that Range.count’s type is Element.Distance, and
> UInt64.Distance is a typealias of … Int. Huh? It’s pretty clear that the
> distance between two UInt64s can’t be represented by a signed Int64. Why
> isn’t Distance UInt64?
Hi Jens,
The distance is signed so that we can represent negative distances.
r.distance(from:to:) should be able to measure distances backwards.
We are aware of this issue, but we don't know of a good solution.
We'd appreciate your suggestions.
Dmitri
--
main(i,j){for(i=2;;i++){for(j=2;j*/
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[swift-users] Range.count can abort
I’m writing some code that deals with ranges of “sequence numbers”, which are consecutively-assigned positive 64-bit integers, thus Range in Swift. I’m having trouble handling half-open ranges with no maximum, which are very commonly used for representing all items created since a certain time. The trouble is, if I represent these with Ranges whose endIndex is UInt64.max, those ranges tend to bomb: let r: Range = 5..___ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
