FlagValue

public protocol FlagValue

Protocol that defines the needs to be implemented for a type to be used as a flag value

Example

Flag with User type

struct User: FlagValue {
  let name: String

  static func fromString(flagValue value: String) throws -> User {
    return User(name: value)
  }

  static var typeDescription: String {
    return "A user structure"
  }
}

We can then use user to define flag type:

let flag = try! Flag(longName: "debug", type: User.self)

  • Create a command string convertible from string

    Throws

    exception thrown if cannot convert from string. The exception of type FlagValueError

    Example

    Create a correct user from string

    struct User: FlagValue {
  let name: String

  static func fromString(flagValue value: String) throws -> User {
    return User(name: value)
  }

  static var typeDescription: String {
    return "A user structure"
  }
}

    Return a parsing error

    struct User: FlagValue {
  let name: String

  static func fromString(flagValue value: String) throws -> User {
    if value == "wrong" {
        throw FlagValueError.conversionError("wrong user passed")
    }
    return User(name: value)
  }

  static var typeDescription: String {
    return "A user structure"
  }
}

    Declaration

    Swift

    static func fromString(flagValue value: String) throws -> Self

    Parameters

    value

    the string to be converted
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  • Return a decription to be printed when priting the command help

    Example

    struct User: FlagValue {
  let name: String

  static func fromString(flagValue value: String) throws -> User {

    return User(name: value)
  }

  static var typeDescription: String {
    return "A user structure"
  }
}

    When printing the help, the typeDescription will be used.

    Flags:
  -u, --user         A user structure

Use "command [command] --help" for more information about a command.

    Declaration

    Swift

    static var typeDescription: String { get }
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