A horrendous example of custom pattern matching in Swift

array_structure.swift

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

import Cocoa

enum Wildcard : NilLiteralConvertible {
  case Single
  case FromBeginning
  case ToEnd
  case Range(Int)
  case Literal(Int)
  init(nilLiteral: ()) {
    self = .Single
  }
}

prefix operator * {}
prefix func *(value: Int) -> Wildcard {
  return Wildcard.Literal(value)
}

prefix operator <~ { }
prefix func <~(value: Wildcard) -> Wildcard {
  return Wildcard.FromBeginning
}

postfix operator ~> { }
postfix func ~>(value: Wildcard) -> Wildcard {
  return Wildcard.ToEnd
}

func ~=(pattern: [Wildcard], value: [Int]) -> Bool {
  var ctr = 0
  for currentPattern in pattern {
    if ctr < 0 || ctr >= value.count { return false }
    let currentValue = value[ctr]
    let currentWildcard = currentPattern
    switch currentWildcard {
    case .Single: ctr++
    case .FromBeginning where ctr == 0:
      ctr = (value.count - pattern.count + 1)
    case .FromBeginning: return false
    case .ToEnd: return true
    case .Range(let r): ctr += r
    case .Literal(let v):
      if v != currentValue { return false }
      else { ctr++ }
    }
  }
  return true
}

// Basic version
let myArray = [1, 2, 4, 3]
switch myArray {
case [.FromBeginning, .Literal(0), .Literal(0), .Literal(0)]:
  "last three elements are 0"
case [Wildcard.Literal(4), Wildcard.ToEnd]:
  "first element is 4, everything else doesn't matter"
case [Wildcard.Single, Wildcard.Literal(2), Wildcard.Single, Wildcard.Literal(4)]:
  "4 elements; second element is 2, fourth element is 4"
case [Wildcard.Range(2), Wildcard.Literal(3), Wildcard.Single]:
  "third element (out of 4) is 3"
case [Wildcard.Range(3), Wildcard.Literal(3)]:
  "fourth element (out of 4) is 3"
default:
  "catchall"
}

// ADVANCED VERSION: custom operator abuse
let anotherArray = [2, 10 ,0, 0, 0]
anotherArray.count
switch anotherArray {
case [<~nil, *0, *0, *0]:
  "last three elements are 0, everything else doesn't matter"
case [*4, nil~>]:
  "first element is 4, everything else doesn't matter"
case [nil, *2, nil, *2]:
  "4 elements; second element is 2, fourth element is 4"
case [nil, nil, *3, nil]:
  "third element (out of 4) is 3"
case [nil, nil, nil, *3]:
  "fourth element (out of 4) is 3"
default:
  "catchall"
}