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

[Hooman Mehr]

> On Oct 12, 2016, at 3:21 AM, Jean-Denis Muys via swift-users <swift-users at swift.org> wrote:
> 
> 
> But this is not very DRY.
> 
> What would be a more idiomatic way?
> 

The more idiomatic way is to look at API design in a new way. Note these points:

1. `Countable` variant is preferred when you want to deal with integer ranges as it more closely matches the element type.
2. Both countable range variants share a common protocol conformance already: `RandomAccessCollection`
3. Swift API design prefers member functions to free functions.

Hence a more idiomatic (Swifty) API would probably be something like this:

extension RandomAccessCollection {
    
    func random() -> Iterator.Element? {
        
        guard count > 0 else { return nil }
        
        let offset = arc4random_uniform(numericCast(count))
        
        let i = index(startIndex, offsetBy: numericCast(offset))
        
        return self[i]
    }
}

Using the above, both cases work and there is no repetition:

(4..<10).random()
(4...9).random()

It also makes a lot more possible: 

let people = ["David", "Chris", "Joe", "Jordan", "Tony"]
let winner = people.random()
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