Conformity to CollectionType simply requires implementing the methods of Indexable.

CollectionType.swift

extension <# extendedType #> : CollectionType {  
  var startIndex: <# indexType : ForwardIndexType #> { return <# startIndex #> }
  var endIndex: <# indexType : ForwardIndexType #> { return <# endIndex #> }
  subscript (index: <# indexType : ForwardIndexType #>) -> <# elementType #> {
    return <# subscript value #>
  }
}