print시 Optional(value)

var num: Int? = 3
print(num)
//결과값: Optional("3")

에서 왜 출력값이 Optional("3")로 나오는지 이유를 찾아보라는 과제를 받았다.
처음 들었을때 뭔 1 + 1이 2인 이유를 증명하라와 비슷한 느낌을 받았는데 좀 찾아보니

@frozen
public enum Optional<Wrapped: ~Copyable>: ~Copyable {
  // The compiler has special knowledge of Optional<Wrapped>, including the fact
  // that it is an `enum` with cases named `none` and `some`.

  /// The absence of a value.
  ///
  /// In code, the absence of a value is typically written using the `nil`
  /// literal rather than the explicit `.none` enumeration case.
  case none

  /// The presence of a value, stored as `Wrapped`.
  case some(Wrapped)
}

일단 옵셔널은 이렇게 case none 과 some(Wrapped)로 이루어진 enum이라는것을 알았다.

@_unavailableInEmbedded
extension Optional: CustomDebugStringConvertible {
  /// A textual representation of this instance, suitable for debugging.
  public var debugDescription: String {
    switch self {
    case .some(let value):
#if !SWIFT_STDLIB_STATIC_PRINT
      var result = "Optional("
      #if !$Embedded
      debugPrint(value, terminator: "", to: &result)
      #else
      _ = value
      "(cannot print value in embedded Swift)".write(to: &result)
      #endif
      result += ")"
      return result
#else
    return "(optional printing not available)"
#endif
    case .none:
      return "nil"
    }
  }
}

이 코드 때문이다

A textual representation of this instance, suitable for debugging

.some case 에서 "Optional(" ")"을 value 앞 뒤로 붙여준 코드다

https://github.com/swiftlang/swift/blob/main/stdlib/public/core/Optional.swift 자세한 내용은 여기로