yeah, which is why I think the at:from: system is better than any subscript alternative. I know everyone wants to use the square brackets but it just doesn’t work very well for exactly the reasons you mentioned.
On Sat, Sep 30, 2017 at 6:07 PM, Dave Abrahams <[email protected]> wrote: > > > On Sep 29, 2017, at 4:03 PM, Taylor Swift <[email protected]> wrote: > > > > On Sep 29, 2017, at 5:56 PM, Dave Abrahams <[email protected]> wrote: > > > > On Sep 29, 2017, at 3:48 PM, Taylor Swift <[email protected]> wrote: > > > > On Fri, Sep 29, 2017 at 4:13 PM, Andrew Trick <[email protected]> wrote: > >> >> >> On Sep 29, 2017, at 1:23 PM, Taylor Swift <[email protected]> wrote: >> >> Instead of >>> >>> buf.intialize(at: i, from: source) >>> >>> We want to force a more obvious idiom: >>> >>> buf[i..<n].intialize(from: source) >>> >>> >> The problem with subscript notation is we currently get the n argument >> from the source argument. So what would really have to be written is >> >> buf[i ..< i + source.count].initialize(from: source) >> >> which is a lot more ugly and redundant. One option could be to decouple >> the count parameter from the length of the source buffer, but that opens up >> the whole can of worms in which length do we use? What happens if n - i is >> less than or longer than source.count? If we enforce the precondition >> that source.count == n - i, then this syntax seems horribly redundant. >> >> >> Sorry, a better analogy would have been: >> >> buf[i...].intialize(from: source) >> >> Whether you specify the slice’s end point depends on whether you want to >> completely initialize that slice or whether you’re just filling up as much >> of the buffer as you can. It also depends on whether `source` is also a >> buffer (of known size) or some arbitrary Sequence. >> >> Otherwise, point taken. >> >> -Andy >> > > After thinking about this more, one-sided ranges might provide just the > expressivity we need. What if: > > buf[offset...].initialize(from: source) // initializes source.count > elements from source starting from offset > > buf[offset ..< endIndex].initialize(from: source) // initializes up to > source.count elements from source starting from offset > > > The one sided one does not give a full initialization guarantee. The two > sided one guarantees the entire segment is initialized. > > > In every other context, x[i...] is equivalent to x[i..<x.endIndex] > > I don't think breaking that precedent is a good idea. > > For move operations, the one sided one will fully deinitialize the source > buffer while the two sided one will only deinitialize endIndex - offset > elements. > > > — > -Dave > > > well since people want to use subscript notation so much we need some way > of expressing case 1. writing both bounds in the subscript seems to imply a > full initialization (and thus partial movement) guarantee. > > > Yes, I understood your reasoning. Do you understand why I still don't > want to proceed in that direction? > > — > -Dave > > > > > >
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