使用闭包作为函数参数时，快速分隔参数不带逗号

Question

In Swift 1.1 with Xcode 6.2, I'd like to understand what is going on here:

ExampleInfo(title: item.title) { self.getItemById(item.uniqueId) }

and why is this the same as:

ExampleInfo(title: item.title, { self.getItemById(item.uniqueId) })

This is what i'm constructing:

class ExampleInfo : NSObject {

    let title : NSString
    var exampleFunc: () -> (UIViewController)

    init(title: NSString, example exampleFunc:() -> (UIViewController)) {
        self.exampleFunc = exampleFunc
        self.title = title
    }
}

Ideally I want to read a part of the documentation that explains why this behavior is allowed and what it's called. (or am I missing something?).

Is this allowed only for closures? (I can see that I am allowed to omit many things with closures, such as brackets and return statements).

tia

Answer 1

that is called a trailing closure . From the official documentation:

If you need to pass a closure expression to a function as the function's final argument and the closure expression is long, it can be useful to write it as a trailing closure instead. A trailing closure is a closure expression that is written outside of (and after) the parentheses of the function call it supports.

Read more in the official documentation here - https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html