ClosedRange 数组<Int>和反向收集<ClosedRange<Int> &gt;

Question

I can easily iterate through the elements of a closed range. Ditto for the elements of the reversed() of a closed range. However, these two constructs happen to have different types, such as ClosedRange<Int> for the former and ReverseCollection<ClosedRange<Int>> .

Suppose I need to have some kind of collection (eg, an array) including both ranges and reversed ranges: how would I go about it?

Example:

let aaa = 1...3
let bbb = (4...6).reversed()
let ranges = [aaa,bbb]  // heterogeneous collection literal could only be inferred of type '[Any]'
for range in ranges {
  for item in range {
    print(item)
  }
}

Simply declaring ranges to be of type [Sequence] or [Collection] does not work, because "Protocol 'Sequence' can only be used as a generic constraint because it has Self or associated type requirements".

Answer 1

You would need to convert all elements to the same type either Array or AnySequence , depending on your performance concerns. Array would create new storage but when the sequence is reversed may have better performance. AnySequence merely forwards operations to its base class, thus depending on your sequence size, could be computationally complex.

let aaa = Array(1...3)
let bbb = Array((4...6).reversed())

let ranges = [aaa, bbb]
for range in ranges {
    for item in range {
        print(item)
    }
}

Answer 2

You can use AnySequence :

let aaa = AnySequence(1...3)
let bbb = AnySequence((4...6).reversed())
let ranges = [aaa, bbb] // ranges is [AnySequence<Int>]
for range in ranges {
  for item in range {
    print(item)
  }
}