patternMatch.swift

struct _Empty<T>: ArrayLiteralConvertible {
  init(arrayLiteral: T...) {
    assert(arrayLiteral.isEmpty)
  }
}

func ~= <C : CollectionType>(lhs: _Empty<C.Generator.Element>, rhs: C) -> Bool {
  return rhs.isEmpty
}

func ~= <T>(lhs: T -> Bool, rhs: T) -> Bool {
  return lhs(rhs)
}

let emptyAr: [Int] = []

switch emptyAr {
case []: print("empty") // "empty"
default: print("not")
}

let nonEmptyAr = [1, 2, 3]

switch nonEmptyAr {
case []: print("empty")
default: print("not")   // "not"
}

let isEven = {(n: Int) -> Bool in n % 2 == 0}

switch 2 {
case isEven: print("even") // "even"
default:     print("odd")
}

switch 3 {
case isEven: print("even")
default:     print("odd") // "odd"
}