Option

Use the @Option wrapper to define a property of your custom command as a command-line option. An option is a named value passed to a command-line tool, like --configuration debug. Options can be specified in any order.

An option can have a default value specified as part of its declaration; options with optional Value types implicitly have nil as their default value. Options that are neither declared as Optional nor given a default value are required for users of your command-line tool.

For example, the following program defines three options:

@main
struct Greet: ParsableCommand {
    @Option var greeting = "Hello"
    @Option var age: Int? = nil
    @Option var name: String

    mutating func run() {
        print("\(greeting) \(name)!")
        if let age {
            print("Congrats on making it to the ripe old age of \(age)!")
        }
    }
}

greeting has a default value of "Hello", which can be overridden by providing a different string as an argument, while age defaults to nil. name is a required option because it is non-nil and has no default value.

$ greet --name Alicia
Hello Alicia!
$ greet --age 28 --name Seungchin --greeting Hi
Hi Seungchin!
Congrats on making it to the ripe old age of 28!

Single-Value Options

• init(name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates a required property that reads its value from a labeled option.

• init<T>(name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates an optional property that reads its value from a labeled option.

• init(wrappedValue: Value, name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates a property with a default value that reads its value from a labeled option.

• init(name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> Value)

  Creates a required property that reads its value from a labeled option, parsing with the given closure.

• init<T>(name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates an optional property that reads its value from a labeled option, parsing with the given closure.

• init(wrappedValue: Value, name: NameSpecification, parsing: SingleValueParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> Value)

  Creates a property with a default value that reads its value from a labeled option, parsing with the given closure.

• struct SingleValueParsingStrategy

  The strategy to use when parsing a single value from @Option arguments.

Array Options

• init<T>(name: NameSpecification, parsing: ArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates a required array property that reads its values from zero or more labeled options.

• init<T>(name: NameSpecification, parsing: ArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates a required array property that reads its values from zero or more labeled options, parsing each element with the given closure.

• init<T>(wrappedValue: Array<T>, name: NameSpecification, parsing: ArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?)

  Creates an array property that reads its values from zero or more labeled options.

• init<T>(wrappedValue: Array<T>, name: NameSpecification, parsing: ArrayParsingStrategy, help: ArgumentHelp?, completion: CompletionKind?, transform: @escaping (String) throws -> T)

  Creates an array property that reads its values from zero or more labeled options, parsing each element with the given closure.

• struct ArrayParsingStrategy

  The strategy to use when parsing multiple values from @Option arguments into an array.

Infrequently Used APIs

• var wrappedValue: Value

  The value presented by this property wrapper.