Swift command design sample – The.Swift.Dev.

The command sample could be helpful in case you’d like to supply a typical interface for various actions that might be executed later in time. Normally it’s an object that encapsulates all the knowledge wanted to run the underlying motion correctly.

Instructions are sometimes used to deal with person interface actions, create undo managers, or handle transactions. Let’s see a command sample implementation in Swift by making a command line argument handler with emojis. 💾

#!/usr/bin/env swift

import Basis

protocol Command {
    func execute()
}

class HelpCommand: Command {

    func execute() {
        Assist().data()
    }
}

class Assist {

    func data() {
        print("""

             🤖 Commander 🤖
                  v1.0

        Obtainable instructions:

            👉 assist      This command
            👉 ls        Listing paperwork

        Bye! 👋

        """)
    }
}

class ListCommand: Command {

    func execute() {
        Listing().homeDirectoryContents()
    }
}

class Listing {

    func homeDirectoryContents() {
        let fileManager = FileManager.default
        guard let documentsURL = fileManager.urls(for: .documentDirectory, in: .userDomainMask).first else {
            print("Couldn't open paperwork listing")
            exit(-1)
        }
        do {
            let fileURLs = strive fileManager.contentsOfDirectory(at: documentsURL, includingPropertiesForKeys: nil)
            print("nt📁 Itemizing paperwork listing:n")
            print(fileURLs.map { "tt💾 " + $0.lastPathComponent }.joined(separator: "nn") + "n" )
        }
        catch {
            print(error.localizedDescription)
            exit(-1)
        }

    }
}

class App {

    var instructions: [String:Command] = [:]

    init() {
        self.instructions["help"] = HelpCommand()
        self.instructions["ls"] = ListCommand()
    }

    func run() {
        let arguments = CommandLine.arguments[1...]

        guard let key = arguments.first, self.instructions[key] != nil else "))]")
            exit(-1)
        

        self.instructions[key]!.execute()
    }
}

App().run()

In the event you save this file, can run it by merely typing ./file-name.swift from a terminal window. The Swift compiler will care for the remainder.

Actual world use instances for the command design sample:

+ numerous button actions
+ assortment / desk view choice actions
+ navigating between controllers
+ historical past administration / undo supervisor
+ transactional conduct
+ progress administration
+ wizards

As you’ll be able to see this sample could be utilized in a number of areas. Apple even made a selected class for this function known as NSInvocation, however sadly it’s not out there in Swift, as a consequence of it’s dynamic conduct. That’s not a giant deal, you’ll be able to at all times make your personal protocol & implementation, most often you simply want one further class that wraps the underlying command logic. 😛