Pastebin: Intを返す関数をNumericに

Formato

C

Post date

2019-11-26 17:25

Publication Period

Unlimited

 struct A {
  var f: () -> Int
 }
 extension A: Equatable {
  static func == (l: A, r: A) -> Bool { l.f() == r.f() }
 }
 extension A: AdditiveArithmetic {
  static let zero = A { 0 }
  static func + (l: A, r: A) -> A { A { l.f() + r.f() } }
  static func += (l: inout A, r: A) {
   let n = l.f()
   l.f = { n + r.f() }
  }
  static func - (l: A, r: A) -> A  { A { l.f() - r.f() } }
  static func -= (l: inout A, r: A) {
   let n = l.f()
   l.f = { n - r.f() }
  }
 }
 extension A: ExpressibleByIntegerLiteral {
  init(integerLiteral value: Int) { f = { value } }
 }
 extension A: Numeric {
  init?<T: BinaryInteger>(exactly source: T) {
   guard let g = Int(exactly: source).map({ s in { s } }) else { return nil }
   f = g
  }
  var magnitude: Int.Magnitude { f().magnitude }
  static func * (l: A, r: A) -> A  { A { l.f() * r.f() } }
  static func *= (l: inout A, r: A) {
   let n = l.f()
   l.f = { n * r.f() }
  }
 }