anothermultisubs.swift

public struct StridingSliceView<C : CollectionType where C.Index : Strideable> : SequenceType {
  
  private let col: C
  private let str: StrideTo<C.Index>
  
  public func generate() -> PermutationGenerator<C, StrideTo<C.Index>> {
    return PermutationGenerator(elements: col, indices: str)
  }
}

public extension CollectionType where Index: Strideable {
  
  public subscript(range: Range<Index>, by: Index.Stride) -> StridingSliceView<Self> {
    return StridingSliceView(col: self, str: stride(from: range.startIndex, to: range.endIndex, by: by))
  }
}

public extension MutableCollectionType where Index : Strideable {
  
  public subscript(range: Range<Index>, by: Index.Stride) -> StridingSliceView<Self> {
    get {
      return StridingSliceView(col: self, str: stride(from: range.startIndex, to: range.endIndex, by: by))
    } set (values) {
      for (index, value) in zip(stride(from: range.startIndex, to: range.endIndex, by: by), values) {
        self[index] = value
      }
    }
  }
}

public extension CollectionType {
  
  public subscript(i1: Index, i2: Index, rest: Index...) ->  PermutationGenerator<Self, [Index]> {
    return PermutationGenerator(elements: self, indices: [i1, i2] + rest)
  }
}

public extension MutableCollectionType {
  
  public subscript(i1: Index, i2: Index, rest: Index...) ->  PermutationGenerator<Self, [Index]> {
    get {
      return PermutationGenerator(elements: self, indices: [i1, i2] + rest)
    } set(values) {
      for (index, value) in zip([i1, i2] + rest, values) {
        self[index] = value
      }
    }
  }
}