This code:
let d0 = Data(bytes: [10, 11, 12, 13, 14, 15])
print(d0[2])
print(d0[3])
let d1 = d0[2...3]
print(d1.count)
print(d1[0])...produces this output in an Xcode 9.3 / Swift 4.1 playground:
12
13
2...and then crashes on the last line:
print(d1[0])...with this error:
error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).
Is this a bug, and if so, any suggestions for a workaround?
if you test :
print(d1[2], d1[3])you get
12 13
So, that shows that indexes still refer to the original array.
It is normal behavior for slices, as documented here :
h ttps://developer.apple.com/documentation/swift/arrayslice
Unlike
ArrayContiguousArrayArraySliceif you test :
print(d1[2], d1[3])you get
12 13
So, that shows that indexes still refer to the original array.
It is normal behavior for slices, as documented here :
h ttps://developer.apple.com/documentation/swift/arrayslice
Unlike
ArrayContiguousArrayArraySliceThanks, that makes sense. But I think the code was working in Swift 4.0 for some reason. Perhaps it shouldn't have been, and now 4.1 fixes this. In my actual implemtation, I pass the range to a function that accepts a Data argument like so:
func f(_ data: Data) {
print(data.startIndex)
}
let d0 = Data(bytes: [10, 11, 12, 13, 14, 15])
let d1 = d0[4...5]
f(d1)
f(Data(d1))Inside function "f" I access the data, and this is where the index behavior has changed, if I'm not mistaken. The playground output from the above is now:
4
0I don't think it worked in 4.0.
I have tried with Swift 3:
let d0 = [10, 11, 12, 13, 14, 15]
let d1 = d0[2...3]
print(d1.count)
print(d1[0])And got the same error (I had to change a bit, as Data does not work in Swift3, but the message is about slice) ; in addition, documentation is cystal clear on the point.
You ask to print startInex, hence you get 4 for d1, that's logical
I think, when you call f(Data(d1)), you just create a new Data, hence startIndex becomes 0
Why do you need to use data and not plain arrays ?
The reason I use Data and not an array is because the actual application where this crash started occurring in Swift 4.1 uses Data for reasons outside the scope of this post. I posted a distilled version of the code here just to illustrate the issue I'm experiencing. Thanks again for your help and insights.