Incorrect error message (UInt8.random and Data)

Using Swift
1

var randomData = Data([UInt8.random(in: 0..<256)])

The compiler flags this as an error because 256 won't fit in a Uint8. Which is correct. But the range is 0..<256 so I should never get back 256.

Right?

2

The issue is that the range type it accepts is Range<UInt8> so in order to make the bounds you need to have a pair of UInt8 of which 256 is not a valid UInt8 in the first place. This is just UInt8.random(in: 0 ... .max)

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3

D'oh! I didn't realize the complaint was about the argument going into the range itself! Thank you so much.

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4

Same here:

for i: Int8 in 0 ..< 128 {} // 🛑 Integer literal '128' overflows when stored into 'Int8'

for this loop to exit i should become equal to 128 at some point, but it can't.

2 Likes
5

A related issue, which has come up on these forums occasionally, is that this code:

for i: UInt8 in 0... {
  print(i)
}

Will print 0 through 254, then crash without ever printing 255.

3 Likes
6

Huh, indeed. Which makes this seemingly equivalent loop different:

var i: UInt8 = 0
while true {
    print(i)
    i += 1
}

(it does print 255 before trapping).

7

@Nevin , @tera: Thank you for the interesting examples.

They crash with different error messages though. @Nevin's example seems to dive deeper. :slight_smile:

// Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

I wonder what the above error message would be on an Apple silicon machine.

// Thread 1: Swift runtime failure: arithmetic overflow
1 Like