# Money **Repository Path**: githubdown/Money ## Basic Information - **Project Name**: Money - **Description**: No description available - **Primary Language**: Unknown - **License**: MIT - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-12-22 - **Last Updated**: 2021-09-01 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README # Money [![Build Status][build status badge]][build status] [![License][license badge]][license] [![Swift Version][swift version badge]][swift version] ![Cocoapods platforms][cocoapods platforms badge] [![Cocoapods compatible][cocoapods badge]][cocoapods] [![Carthage compatible][carthage badge]][carthage] A precise, type-safe representation of monetary amounts in a given currency. This functionality is discussed in Chapter 3 of [Flight School Guide to Swift Numbers](https://flight.school/books/numbers). ## Requirements - Swift 4.0+ ## Installation ### Swift Package Manager Add the Money package to your target dependencies in `Package.swift`: ```swift import PackageDescription let package = Package( name: "YourProject", dependencies: [ .package( url: "https://github.com/Flight-School/Money", from: "1.2.1" ), ] ) ``` Then run the `swift build` command to build your project. ### CocoaPods You can install `Money` via CocoaPods, by adding the following line to your `Podfile`: ```ruby pod 'Money-FlightSchool', '~> 1.2.1' ``` Run the `pod install` command to download the library and integrate it into your Xcode project. > **Note** > The module name for this library is "Money" --- > that is, to use it, you add `import Money` to the top of your Swift code > just as you would by any other installation method. > The pod is called "Money-FlightSchool" > because there's an existing pod with the name "Money". ### Carthage To use `Money` in your Xcode project using Carthage, specify it in `Cartfile`: ``` github "Flight-School/Money" ~> 1.2.1 ``` Then run the `carthage update` command to build the framework, and drag the built Money.framework into your Xcode project. ## Usage ### Creating Monetary Amounts The `Money` type has a required associated `Currency` type. These currency types are named according to their three letter [ISO 4701][iso4217] currency codes. You can initialize a monetary using a `Decimal` value: ```swift let amount = Decimal(12) let monetaryAmount = Money(amount) ``` You can also create monetary amounts using integer, floating-point, and string literals. ```swift 12 as Money 12.00 as Money "12.00" as Money ``` **Important**: Swift floating-point literals are currently initialized using binary floating-point number type, which cannot precisely express certain values. As a workaround, monetary amounts initialized from a floating-point literal are rounded to the number of places of the minor currency unit. If you want to express a smaller fractional monetary amount, initialize from a string literal or `Decimal` value instead. ```swift let preciseAmount: Money = "123.4567" let roundedAmount: Money = 123.4567 preciseAmount.amount // 123.4567 roundedAmount.amount // 123.46 ``` For more information, see https://bugs.swift.org/browse/SR-920. ### Comparing Monetary Amounts You can compare two monetary amounts with the same currency: ```swift let amountInWallet: Money = 60.00 let price: Money = 19.99 amountInWallet >= price // true ``` Attempting to compare monetary amounts with different currencies results in a compiler error: ```swift let dollarAmount: Money = 123.45 let euroAmount: Money = 4567.89 dollarAmount == euroAmount // Error: Binary operator '==' cannot be applied ``` ### Adding, Subtracting, and Multiplying Monetary Amounts Monetary amounts can be added, subtracted, and multiplied using the standard binary arithmetic operators (`+`, `-`, `*`): ```swift let prices: [Money] = [2.19, 5.39, 20.99, 2.99, 1.99, 1.99, 0.99] let subtotal = prices.reduce(0.00, +) // "$36.53" let tax = 0.08 * subtotal // "$2.92" let total = subtotal + tax // "$39.45" ``` **Important**: Multiplying a monetary amount by a floating-point number results in an amount rounded to the number of places of the minor currency unit. If you want to produce a smaller fractional monetary amount, multiply by a `Decimal` value instead. ### Formatting Monetary Amounts You can create a localized representation of a monetary amount using `NumberFormatter`. Set the `currencyCode` property of the formatter to the `currency.code` property of the `Money` value and pass the `amount` property to the formatter `string(for:)` method. ```swift let allowance: Money = 10.00 let formatter = NumberFormatter() formatter.numberStyle = .currency formatter.locale = Locale(identifier: "fr-FR") formatter.currencyCode = allowance.currency.code formatter.string(for: allowance.amount) // "10,00 $US" ``` ### Encoding and Decoding Monetary Amounts #### Encoding By default, `Money` values are encoded as keyed containers, with `amount` encoded as a number value. ```swift let value: Money = 123.45 let encoder = JSONEncoder() let data = try encoder.encode(value) String(data: data, encoding: .utf8) // #"{"amount":123.45,"currencyCode":"USD"}"# ``` To configure encoding behavior, set either the `JSONEncoder.moneyEncodingOptions` property or the `CodingUserInfoKey.moneyEncodingOptions` key in the encoder's `userInfo` property. ```swift var encoder = JSONEncoder() encoder.moneyEncodingOptions = [.omitCurrency, .encodeAmountAsString] let data = try encoder.encode([value]) String(data: data, encoding: .utf8) // #"["123.45"]"# ``` #### Decoding The default decoding behavior is flexible, supporting both keyed and single value containers, with string or number values for `amount`. ```swift let json = #""" [ { "currencyCode": "USD", "amount": "100.00" }, 50.00, "10" ] """#.data(using: .utf8)! let decoder = JSONDecoder() let values = try decoder.decode([Money].self, from: json) values.first?.amount // 100.00 values.last?.currency.code // "USD" ``` To configure decoding behavior, set either the `JSONDecoder.moneyDecodingOptions` property or the `CodingUserInfoKey.moneyDecodingOptions` key in the decoder's `userInfo` property. ```swift var decoder = JSONDecoder() decoder.moneyDecodingOptions = [.requireExplicitCurrency] ``` **Important**: Foundation decoders currently decode number values using a binary floating-point number type, which cannot precisely express certain values. As a workaround, you can specify the `requireStringAmount` decoding option to require monetary amounts to be decoded precisely from a string representation. ```swift let json = #""" { "currencyCode": "USD", "amount": "27.31" } """#.data(using: .utf8)! var decoder = JSONDecoder() try decoder.decode(Money.self, from: json) // DecodingError decoder.moneyDecodingOptions = [.requireStringAmount] let preciseAmount = try decoder.decode(Money.self, from: json) preciseAmount.amount // 27.31 ``` Alternatively, you can the `roundFloatingPointAmount` decoding option to round decoded floating-point values to the number of places of the minor currency unit. ```swift let json = #""" { "currencyCode": "USD", "amount": 27.31 } """#.data(using: .utf8)! var decoder = JSONDecoder() let impreciseAmount = try decoder.decode(Money.self, from: json) impreciseAmount.amount // 27.30999999... decoder.moneyDecodingOptions = [.roundFloatingPointAmount] let roundedAmount = try decoder.decode(Money.self, from: json) roundedAmount.amount // 27.31 ``` For more information, see https://bugs.swift.org/browse/SR-7054. ### Supporting Multiple Currencies Consider a `Product` structure with a `price` property. If you only support a single currency, such as US Dollars, you would define `price` to be of type `Money`: ```swift struct Product { var price: Money } ``` If you want to support multiple currencies, however, you can't specify an explicit currency type in the property declaration. Instead, the `Product` would have to be defined as a generic type: ```swift struct Product { var price: Money } ``` Unfortunately, this approach is unwieldy, as each type that interacts with `Product` would also need to be generic, and so on, until the entire code base is generic over the currency type. ```swift class ViewController : UIViewController { ... } // 😭 ``` A better solution would be to define a new `Price` protocol with requirements that match the `Money` type: ```swift protocol Price { var amount: Decimal { get } var currency: CurrencyType.Type { get } } extension Money: Price {} ``` Doing this allows prices to be defined in multiple currencies without making `Product` generic over the currency type: ```swift struct Product { var price: Price } let product = Product(price: 12.00 as Money) product.price // "$12.00" ``` If you want to support only certain currencies, such as US Dollars and Euros, you can define a `SupportedCurrency` protocol and add conformance to each currency type through an extension: ```swift protocol SupportedCurrency: CurrencyType {} extension USD: SupportedCurrency {} extension EUR: SupportedCurrency {} extension Money: Price where Currency: SupportedCurrency {} ``` Now, attempting to create a `Product` with a price in an unsupported currency results in a compiler error: ```swift Product(price: 100.00 as Money) Product(price: 100.00 as Money) // Error ``` #### Supported Currencies This package provides a `Currency` type for each of the currencies defined by the [ISO 4217][iso4217] standard with the exception of special codes, such as USN (US Dollar, Next day) and XBC (Bond Markets Unit European Unit of Account 9). The [source file][currency.swift] defining the available currencies is generated from a [CSV file][iso4217.csv] using [GYB][gyb]. This data source is up-to-date with [ISO 4217 Amendment Number 169](https://www.currency-iso.org/en/shared/amendments/iso-4217-amendment.html), published on August 17, 2018. You can regenerate `Sources/Money/Currency.swift` from `Resources/iso4217.csv` by installing [GYB][gyb] and running the `make` command from the terminal: ```terminal $ make ``` > We don't currently have a mechanism to automatically update this data source. > Please [open an issue](https://github.com/Flight-School/Money/issues/new) > if you're aware of any new amendments made to ISO 4217. ### Adding Custom Currencies You can create your own custom currency types by defining an enumeration that conforms to the `CurrencyType` protocol. For example, here's how you might represent Bitcoin (BTC): ```swift enum BTC: CurrencyType { static var name: String { return "Bitcoin" } static var code: String { return "BTC" } static var minorUnit: Int { return 8 } } let satoshi: Money = 0.00000001 ``` `NumberFormatter` only supports currencies defined by ISO 4217, so you'll have to configure the symbol, currency code, and any other necessary parameters: ```swift let formatter = NumberFormatter() formatter.numberStyle = .currency formatter.currencySymbol = "₿" formatter.currencyCode = "BTC" formatter.maximumFractionDigits = 8 formatter.string(for: satoshi.amount) // ₿0.00000001 ``` ### Showing Off with Emoji If you're the type of person who enjoys putting clip art in your source code, here's a trick that'll _really_ impress your teammates: ```swift typealias 💵 = Money typealias 💴 = Money typealias 💶 = Money typealias 💷 = Money let tubeFare: 💷 = 2.40 // "£2.40" ``` ## Alternatives to Consider A type-safe `Money` structure like the one provided by this package can reduce the likelihood of certain kinds of programming errors. However, you may find the cost of using this abstraction to outweigh the benefits it can provide in your code base. If that's the case, you might consider implementing your own simple `Money` type with a nested `Currency` enumeration like this: ```swift struct Money { enum Currency: String { case USD, EUR, GBP, CNY // supported currencies here } var amount: Decimal var currency: Currency } ``` It's ultimately up to you to decide what kind of abstraction is best for your particular use case. Whatever you choose, just make sure to represent monetary amounts using a `Decimal` type with an explicit currency. ## License MIT ## Contact Mattt ([@mattt](https://twitter.com/mattt)) [build status]: https://github.com/Flight-School/Money/actions?query=workflow%3ACI [build status badge]: https://github.com/Flight-School/Money/workflows/CI/badge.svg [currency.swift]: https://github.com/Flight-School/Money/blob/master/Sources/Money/Currency.swift [iso4217]: https://en.wikipedia.org/wiki/ISO_4217 [iso4217.csv]: https://github.com/Flight-School/Money/blob/master/Resources/iso4217.csv [gyb]: https://nshipster.com/swift-gyb/ [license]: https://opensource.org/licenses/MIT [license badge]: https://img.shields.io/cocoapods/l/Money-FlightSchool.svg [swift version]: https://swift.org/download/ [swift version badge]: https://img.shields.io/badge/swift%20version-4.0+-orange.svg [cocoapods platforms badge]: https://img.shields.io/cocoapods/p/Money-FlightSchool.svg [cocoapods]: https://cocoapods.org/pods/Money-FlightSchool [cocoapods badge]: https://img.shields.io/cocoapods/v/Money-FlightSchool.svg [carthage]: https://github.com/Carthage/Carthage [carthage badge]: https://img.shields.io/badge/Carthage-compatible-4BC51D.svg