CODEWITHSUNDEEP
swift
Devarshi
Devarshi

Reputation: 16758

Is it possible to use multiple trailing closures in swift?

I know it is possible to define methods which accept closures like this:

A. Single closure as input parameter

func testOfClosures (flag: Int, closure1: () -> ())
{
     closure1()
}

B. Multiple closures as input parameters

func testOfClosures (flag: Int, closure1: () -> (), closure2: () -> (), closure3: () ->  ())
{
    switch flag
    {
        case 1:
             closure1()
        case 2:
             closure2()
        default:
             closure3()
    }
}

Interestingly in first case we can invoke it like this:

testOfClosures(1){
    println("print closure 1")
}

but in second case, we cannot invoke it like this:

testOfClosures(1,{
    println("print closure 1")
},
{
    println("print closure 2")
})
{
    println("print closure 3")
}

and we have to invoke it like this:

testOfClosures(1,{
    println("print closure 1")
},
{
    println("print closure 2")
},
{
    println("print closure 3")
})

Any reasons?

Upvotes: 5

Views: 4622

Answers (2)

BilalReffas
BilalReffas

Reputation: 8328

Yes you can do it since Swift 5.3.

Please see this example 

// Multiple trailing closure arguments
UIView.animate(withDuration: 0.3) {
  self.view.alpha = 0
} completion: { _ in
  self.view.removeFromSuperview()
}

Credit and more infos from this Proposal

Upvotes: 6

Bryan McLemore
Bryan McLemore

Reputation: 6493

It looks like the trailing closure syntax is very specific about the position of the opening { and requires it to be on the same line as the closing )

The below works

testOfClosures(1,{
    println("print closure 1")
},
{
    println("print closure 2")
}) {
    println("print closure 3")
}

As far as multiple trailing closures, that is not possible. The documentation specifically states only the final closure as using the special syntax.

Upvotes: 4

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