# [swift-users] How to be DRY on ranges and closed ranges?

Hooman Mehr hooman.mehr at gmail.com
Wed Oct 12 18:16:33 CDT 2016

```I recommend having explicit precondition and reducing repetition like this:

import Foundation

func random(from range: CountableRange<Int>) -> Int {

precondition(range.count > 0,
"The range can't be empty.")

return random(from: CountableClosedRange(range))
}

func random(from range: CountableClosedRange<Int>) -> Int {

let lowerBound = range.lowerBound
let upperBound = range.upperBound

precondition(upperBound - lowerBound < Int(UInt32.max),
"The range \(range) is too wide. It shouldn't be wider than \(UInt32.max).")

return lowerBound + Int(arc4random_uniform(UInt32(upperBound - lowerBound + 1)))
}

let r1 = random(from: 4 ..< 8)
let r2 = random(from: 6 ... 8)

Once we have the new improved Integer protocols <https://github.com/apple/swift-evolution/blob/master/proposals/0104-improved-integers.md> in place, you will be able to make it generic to support all integer types. (It is possible now, but too messy to be worth doing.)

> On Oct 12, 2016, at 1:23 PM, Adriano Ferreira via swift-users <swift-users at swift.org> wrote:
>
> Hi there!
>
> Ole Begeman offers here <https://oleb.net/blog/2016/09/swift-3-ranges/> (take a look at the bottom of the page) an interesting consideration about converting between half-open and closed ranges.
>
> As of now, it seems the way to go is by overloading…
>
>
> import Foundation
>
> func random(from range: Range<Int>) -> Int {
>     let lowerBound = range.lowerBound
>     let upperBound = range.upperBound
>
>     return lowerBound + Int(arc4random_uniform(UInt32(upperBound - lowerBound)))
> }
>
> func random(from range: ClosedRange<Int>) -> Int {
>     let lowerBound = range.lowerBound
>     let upperBound = range.upperBound
>
>     return lowerBound + Int(arc4random_uniform(UInt32(upperBound - lowerBound + 1)))
> }
>
> let r1 = random(from: 4 ..< 8)
> let r2 = random(from: 6 ... 8)
>
>
> Cheers,
>
> — A
>
>> On Oct 12, 2016, at 6:21 AM, Jean-Denis Muys via swift-users <swift-users at swift.org <mailto:swift-users at swift.org>> wrote:
>>
>> Hi,
>>
>> I defined this:
>>
>> func random(from r: Range<Int>) -> Int {
>>     let from = r.lowerBound
>>     let to =  r.upperBound
>>
>>     let rnd = arc4random_uniform(UInt32(to-from))
>>     return from + Int(rnd)
>> }
>>
>> so that I can do:
>>
>> let testRandomValue = random(from: 4..<8)
>>
>> But this will not let me do:
>>
>> let otherTestRandomValue = random(from: 4...10)
>>
>> The error message is a bit cryptic:
>>
>> “No ‘…’ candidate produce the expected contextual result type ‘Range<Int>’”
>>
>> What is happening is that 4…10 is not a Range, but a ClosedRange.
>>
>> Of course I can overload my function above to add a version that takes a ClosedRange.
>>
>> But this is not very DRY.
>>
>> What would be a more idiomatic way?
>>
>> Thanks,
>>
>> Jean-Denis
>>
>> _______________________________________________
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>> swift-users at swift.org <mailto:swift-users at swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-users
>
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