doihatethis.swift

//: Playground - noun: a place where people can play

import UIKit

// Test data
let x = ["a", "b", "c", "d", "e"]
let y = "Hello world"

/*
  Unsafe index manipulation: can return invalid results
  since the index is manipulated without regard to the 
  underlying instance
*/
func +<Index: ForwardIndexType>(idx: Index, distance: Index.Distance) -> Index {
    return idx.advancedBy(distance)
}

func -<Index: BidirectionalIndexType>(idx: Index, distance: Index.Distance) -> Index {
    return idx.advancedBy(-distance)
}

/*
  Safer indexing, takes end index into account for forward indexing
  and start index for backwards indexing
*/
infix operator -->> {}
func -->><C:CollectionType where C.Index: BidirectionalIndexType>  (collection: C, distance: C.Index.Distance) -> C.Index {
    return collection.startIndex.advancedBy(distance, limit: collection.endIndex.predecessor())
}

infix operator ->> {}
func ->><C:CollectionType where C.Index: BidirectionalIndexType>  (collection: C, distance: C.Index.Distance) -> C.Generator.Element {
    return collection[collection -->> distance]
}

infix operator <<-- {}
func <<--<C:CollectionType where C.Index: BidirectionalIndexType>  (collection: C, distance: C.Index.Distance) -> C.Index {
    return collection.endIndex.predecessor().advancedBy(-distance, limit: collection.startIndex)
}

infix operator <<- {}
func <<-<C:CollectionType where C.Index: BidirectionalIndexType>  (collection: C, distance: C.Index.Distance) -> C.Generator.Element {
    return collection[collection <<-- distance]
}

// e.g.
y.substringFromIndex(y.startIndex + 3)
y.substringToIndex(y.endIndex - 3)