String拡張のカスタムinitを追加するには？

Question

String拡張のカスタムinitメソッドを追加するにはどうしたらいいですか？ UPDATED

let price = Double(155.15) 
let formattedPrice = String(price, decimalPlaces: 2) // formattedPrice = "$155.15" 

：値型の初期化子（および変異メソッドは）単純に割り当てることができる最終的な解決策

extension String { 
    init?(currencyAmount: Double) { 
     let formatter = NumberFormatter() 
     formatter.numberStyle = .currency 
     formatter.locale = Locale(identifier: NSLocalizedString("Defaults.LocaleCurrencyFormat", comment: "currency sign")) // Defaults.LocaleCurrencyFormat equal "es_US" for US 
     let formattedAmount = formatter.string(from: NSNumber(value: currencyAmount)) ?? "" 
     self.init(formattedAmount) 
    } 
} 

Answer 1

私はこのような何かを見たいと思ってその結果

extension String { 
    init(_ amount: Double, decimalPlaces: UInt) { 
     self.init() 
     let decimalFormat = "%0.\(String(decimalPlaces))f" 
     let currencyAmount = String(format: decimalFormat, amount) 
     let currencySign = NSLocalizedString("Defaults.CurrencySign", comment: "currency sign") 
     let formattedString = "\(currencySign)\(currencyAmount)" 
     // How to set self to `formattedString` ? 
    } 
} 

直接selfに：

import Foundation 

extension String { 
    init(_ amount: Double, decimalPlaces: UInt) { 
     let currencyAmount = String(format: "%\(decimalPlaces).f", amount) 
     let currencySign = NSLocalizedString("Defaults.CurrencySign", comment: "currency sign") 
     self = "\(currencySign)\(currencyAmount)" 
    } 
} 

let price = Double(155.15) 
let formattedPrice = String(price, decimalPlaces: 2) // formattedPrice = "$155.15"