NEW: Get your ticket for Hacking with Swift Live 2019! >>

< Previous: Using closures as parameters when they return values   Next: Closures with multiple parameters >

Shorthand parameter names

We just made a travel() function. It accepts one parameter, which is a closure that itself accepts one parameter and returns a string. That closure is then run between two calls to print().

Here’s that in code:

func travel(action: (String) -> String) {
    print("I'm getting ready to go.")
    let description = action("London")
    print(description)
    print("I arrived!")
}

We can call travel() using something like this:

travel { (place: String) -> String in
    return "I'm going to \(place) in my car"
}

However, Swift knows the parameter to that closure must be a string, so we can remove it:

travel { place -> String in
    return "I'm going to \(place) in my car"
}

It also knows the closure must return a string, so we can remove that:

travel { place in
    return "I'm going to \(place) in my car"
}

As the closure only has one line of code that must be the one that returns the value, so Swift lets us remove the return keyword too:

travel { place in
    "I'm going to \(place) in my car"
}

Swift has a shorthand syntax that lets you go even shorter. Rather than writing place in we can let Swift provide automatic names for the closure’s parameters. These are named with a dollar sign, then a number counting from 0.

travel {
    "I'm going to \($0) in my car"
}

UPGRADE YOUR SWIFT Hacking with Swift Live is a new iOS conference taking place in the UK this July, with all profits going to charity. Come and learn the major new APIs announced at WWDC19 with sessions and hands-on tutorials – click here to learn more!

< Previous: Using closures as parameters when they return values   Next: Closures with multiple parameters >
MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let me know!

Average rating: 4.3/5

Click here to visit the Hacking with Swift store >>