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

  • 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