Day 6 of 100 days of SwiftUI

Day 5 of HackingWithSwift's 100 days of SwiftUI. Today I learnt about closures.

You can think of closures as nameless functions that you can assign to a variable or pass as a parameter into a function.
Closures are mostly used to perform an action later in the future when a condition is met. For example, when a file downloads successfully, store its content into a database.

let helloWorldClosure = {
  print("hello")
}

helloWorldClosure()

The code above creates a closure that prints "Hello" and assigns the closure to the helloWorldClosure variable. You can then simply call the closure as you would a function.

let greatClosure = { (name: String) in
   print("Hello \(name)")
}

greatClosure("Sanmi")

The code above creates a closure that takes a single parameter and greats the user. Please note you don't need to add a label when calling a closure.

let addClosure = { (first: Int, second: Int) -> Int in 
    return first + second
}

let sum = addClosure(1,2)

The code above creates a closure that takes two numbers as parameters and returns the sum of the numbers.

Like I said before you can pass closures as a parameter into a function.

let saveFile = {
   //code to save file
}

func downloadFile(imageUrl, onSuccess: () ->) {
  //code to download file
  if(downloadSuccessfull){
     onSuccess()
  }
}

downloadFile(imageUrl: "Instagram", onSuccess: saveFile)

The code above creates a closure that saves a file downloaded from the internet. This closure is passed into the downloadFile function. This downloadFile function downloads a file from the internet and calls the save file closure if the file was downloaded successfully.

If you are interested in taking the challenge, you can find it at https://www.hackingwithswift.com/100/swiftui
See you tomorrow ;)