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Type-safe command line argument handling
.package(url: "https://github.com/Carthage/Commandant.git", from: "0.18.0")


Commandant is a Swift framework for parsing command-line arguments, inspired by Argo (which is, in turn, inspired by the Haskell library Aeson).

Reviewed by Hound


With Commandant, a command and its associated options could be defined as follows:

struct LogCommand: CommandProtocol {
	typealias Options = LogOptions

	let verb = "log"
	let function = "Reads the log"

	func run(_ options: Options) -> Result<(), YourErrorType> {
		// Use the parsed options to do something interesting here.
		return ()

struct LogOptions: OptionsProtocol {
	let lines: Int
	let verbose: Bool
	let logName: String

	static func create(_ lines: Int) -> (Bool) -> (String) -> LogOptions {
		return { verbose in { logName in LogOptions(lines: lines, verbose: verbose, logName: logName) } }

	static func evaluate(_ m: CommandMode) -> Result<LogOptions, CommandantError<YourErrorType>> {
		return create
			<*> m <| Option(key: "lines", defaultValue: 0, usage: "the number of lines to read from the logs")
			<*> m <| Option(key: "verbose", defaultValue: false, usage: "show verbose output")
			<*> m <| Argument(usage: "the log to read")

Then, each available command should be added to a registry:

let commands = CommandRegistry<YourErrorType>()

After which, arguments can be parsed by simply invoking the registry:

var arguments = CommandLine.arguments

// Remove the executable name.
arguments.remove(at: 0)

if let verb = arguments.first {
	// Remove the command name.
	arguments.remove(at: 0)

	if let result = commands.run(command: verb, arguments: arguments) {
		// Handle success or failure.
	} else {
		// Unrecognized command.
} else {
	// No command given.

For real-world examples, see the implementation of the Carthage command-line tool.


Commandant is released under the MIT license.


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Last commit: 19 weeks ago

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Release Notes

31 weeks ago

This release drops support for Swift 5.0-5.1. Only Swift 5.2+ is now supported.

  • ✨ Support for Apple Silicon (arm64) Macs (#158). Thanks, @chris-araman!

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