CODEWITHSUNDEEP
swiftclosures
1789040
1789040

Reputation: 579

Necessity of -> Void in Swift

In the following code (using the Parse library), I have:

query.findObjectsInBackgroundWithBlock({(objects: [AnyObject]?, error: NSError?) -> Void in
    // yada yada
})

Is the -> Void in necessary in the code (rather, is there something else I can use? Removing it throws errors in Xcode.)?

I am very new to Swift, so this may be a dumb question...

Upvotes: 3

Views: 3106

Answers (2)

Taylor M
Taylor M

Reputation: 1865

This -> Void in is saying the closure is not returning anything and what follows the in is the body of the closure. The -> Void can be removed because Swift is very good at inferring types. The in is necessary.

The start of the closure’s body is introduced by the in keyword. This keyword indicates that the definition of the closure’s parameters and return type has finished, and the body of the closure is about to begin.

You can go read more about closures here: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html

Upvotes: 0

matt
matt

Reputation: 536028

The in line is how you get the parameters into the block:

(objects: [AnyObject]?, error: NSError?) -> Void in

If the types are known in some other way, you can omit them:

objects, error in

But you cannot omit the in line entirely unless you pick up the parameters in some other way in your code (as $0 and $1), and that would make your code difficult to understand. It's better to keep the in line so you know what the parameters are.

Upvotes: 3

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