CODEWITHSUNDEEP
iosswiftios8grand-central-dispatchdispatch-async
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Reputation: 443

Passing an argument to dispatch_async

I'm new to Swift and looking at how the dispatch_async function works. The API doc shows dispatch_async having two parameters. However, I'm able to pass in one argument and it's okay. 

dispatch_async(dispatch_get_main_queue()) { 

}

How come I don't need to pass in two arguments?

Thank you,

API Doc:

enter image description here

Upvotes: 1

Views: 2016

Answers (2)

Apple_iOS0304
Apple_iOS0304

Reputation: 1102

This is how the dispatch_async looks like..

dispatch_async(dispatch_get_main_queue(), ^{

});

this part 

^{

}

is the second parameter to your function, which is an anonymous code block used for callBack implementation.

Upvotes: 1

Mikhail Seryukov
Mikhail Seryukov

Reputation: 142

It is a trailing closure syntax

func someFunctionThatTakesAClosure(closure: () -> ()) {
    // function body goes here
}

// here's how you call this function without using a trailing closure:

someFunctionThatTakesAClosure({
    // closure's body goes here
})

// here's how you call this function with a trailing closure instead:

someFunctionThatTakesAClosure() {
    // trailing closure's body goes here
}

https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html

Upvotes: 2

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