SOLVED: How to have trailing closure for function of type (first: () -> Void, second: String) -> Void

@abbas_s_dhd

Mar 26

Hi! I was reading about trailing closures, and I have a doubt.

func doImportantWork(first: () -> Void, second: String) {
    print("About to start first work")
    first()
    print("About to start second work")
}

Can this function be called using trailing closure syntax?

@Obelix

Mar 26

@abbas asks:

Can this function be called using trailing closure syntax?

In @twoStraws' lesson on trailing closures he give an example similar to yours.

Here's a quote from his lesson:

If the last parameter to a function is a closure, Swift lets you use special
syntax called trailing closure syntax. Rather than pass in your closure as a parameter,
you pass it directly after the function inside braces.

Take a close look at your doImportantWork function's parameters. Look closer!

What is the last parameter of your function?

See -> Trailing Closure Syntax

@NigelGee HWS+

Mar 27

You can call this like

func doImportantWork(first: () -> Void, second: String) {
    print("About to start first work")
    first()
    print("About to start second work")
    print("\(second) work done!")
}

func printFirst() {
    print("First work done!")
}

doImportantWork(first: printFirst, second: "Second")

However to get a trailing closure you need to change the first so that it trailing

func doImportantWork(second: String, first: () -> Void) {
    print("About to start first work")
    first()
    print("About to start second work")
    print("\(second) work done!")
}

doImportantWork(second: "Second") {
    print("First work done!")
}

You can even have multiples trailing closures

func doImportantWork(first: () -> Void, second: (String) -> Void) {
    print("About to start first work")
    first()
    print("About to start second work")
    second("Second")
}

doImportantWork {
    print("First work done!")
} second: { string in
    print("\(string) work done!")
}

or even more

func doImportantWork(first: () -> Void, second: (String) -> Void, third: (Int, String) -> Void) {
    print("About to start first work")
    first()
    print("About to start second work")
    second("Second")
    print("About to start third work")
    third(3, "Third")
}

doImportantWork {
    print("First work done!")
} second: { string in
    print("\(string) work done!")
} third: { number, string in
    print("\(number). \(string) work done!")
}

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