Swift compact() for SequenceType

SequenceType+compact.swift

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

import Foundation


protocol OptionalParasite {
	typealias WrappedParasite
	
	func toArray() -> [WrappedParasite]
}
extension Optional: OptionalParasite {
	typealias WrappedParasite = Wrapped
	
	func toArray() -> [WrappedParasite] {
		return flatMap { [$0] } ?? []
	}
}
extension ImplicitlyUnwrappedOptional: OptionalParasite {
	typealias WrappedParasite = Wrapped
	
	func toArray() -> [WrappedParasite] {
		return flatMap { [$0] } ?? []
	}
}


extension SequenceType where Generator.Element: OptionalParasite {
	func compact() -> [Generator.Element.WrappedParasite] {
		return flatMap { element in
			return element.toArray()
		}
	}
}


let abc: [Int?] = [
	54,
	46,
	nil,
	22,
	1,
	nil
]

abc.compact()
// [54, 46, 22, 1]

Here is a version that works with swift 4.2:

protocol OptionalParasite {
  associatedtype WrappedParasite

  func toArray() -> [WrappedParasite]
}

extension Optional: OptionalParasite {
  typealias WrappedParasite = Wrapped

  func toArray() -> [WrappedParasite] {
    return flatMap { [$0] } ?? []
  }
}

extension Sequence where Iterator.Element: OptionalParasite {
  func compact() -> [Iterator.Element.WrappedParasite] {
    return flatMap { element in
      return element.toArray()
    }
  }
}

let abc: [Int?] = [
  54,
  46,
  nil,
  22,
  1,
  nil
]

let foo = abc.compact()