CustomStringConvertible

CustomStringConvertible이란 무엇인가요?

기본 출력은 보기 좋지 않습니다

struct Point { let x: Int; let y: Int }
print(Point(x: 1, y: 2))  // Point(x: 1, y: 2)

description 추가하기

struct Point: CustomStringConvertible {
    let x: Int
    let y: Int
    var description: String { "(\(x), \(y))" }
}
print(Point(x: 1, y: 2))  // (1, 2)

print와 String(describing:)에서 사용됨

struct Money: CustomStringConvertible {
    let cents: Int
    var description: String { "$\(Double(cents) / 100)" }
}
let m = Money(cents: 250)
print("price is \(m)")  // price is $2.5

description과 직접 만든 프로퍼티 비교

열거형 형식 지정하기

enum Suit: CustomStringConvertible {
    case hearts, spades
    var description: String {
        switch self {
        case .hearts: return "Hearts"
        case .spades: return "Spades"
        }
    }
}
print(Suit.hearts)  // Hearts

description 조합하기

struct Card: CustomStringConvertible {
    let rank: Int
    let suit: String
    var description: String { "\(rank) of \(suit)" }
}
let cards = [Card(rank: 1, suit: "H"), Card(rank: 13, suit: "S")]
print(cards.map { $0.description })  // ["1 of H", "13 of S"]

컬렉션 내부에서 사용하기

struct Tag: CustomStringConvertible {
    let name: String
    var description: String { "#\(name)" }
}
print([Tag(name: "swift"), Tag(name: "ios")])  // [#swift, #ios]

문자열 보간은 description을 사용합니다

struct Temperature: CustomStringConvertible {
    let celsius: Int
    var description: String { "\(celsius)C" }
}
let t = Temperature(celsius: 21)
print("Now: \(t)")  // Now: 21C

비용을 낮게 유지하기

struct ID: CustomStringConvertible {
    let value: Int
    var description: String { "ID#\(value)" }
}
print(ID(value: 42))  // ID#42

조건부 형식 지정

struct Stock: CustomStringConvertible {
    let count: Int
    var description: String {
        count == 0 ? "Out of stock" : "\(count) in stock"
    }
}
print(Stock(count: 0))  // Out of stock
print(Stock(count: 5))  // 5 in stock

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