Hello,
> The collection is a subject which has elements, and we are asking for one of
> them at random.
it has elements, sure.
And because of its structure, it has a first and a last element and whatever.
But that random element is not an inherent property of the collection.
I find it much more natural to use the random number generator to draw random
elements from collections than the other way round.
That approach also completely side-steps the problem with having to define
default arguments. The user can just use any random number generator she has.
Obviously, it makes sense to provide a default one named `random` to make it
easily accessible.
>>> var list = [1,2,3,4]
>>> let a:Int? = list.randomElement //List is still [1,2,3,4] and ‘a’ contains
>>> one of the elements
>>
>> Instead I would prefer to have something like:
>>
>> let a = random.draw(from: list)
>
> But now the RNG has to understand the concept of collections. I would argue
> it is much cleaner to write an extension on Collection.
>
> func randomElement(using source: RandomSource = .default) -> Element? {
> guard !isEmpty else {return nil}
> let idx = Int.random(in: 0…(count - 1), using: source)
> return self[idx]
> }
But then the Collection has to understand the concept of random numbers. ;-)
Well both approaches are equally clean from this point of view:
extension RandomFoo {
func draw<T: Collection>(from urn: T) -> T.Element? {
guard !urn.isEmpty else { return nil }
let idx = draw(from: urn.indices)
return urn[idx]
}
}
We just have to define one base protocol for such extensions. Every random
number generator then automatically knows how to draw elements from ranges and
collections.
— Martin
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