00. Three forms of Closures

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Swift › 02. Closures

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As the Apple official documents says, closures take one of three forms:

1. Global functions

Global functions are closures that have a name and don’t capture any values.

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func setupBlock {
    print("Hello")
}

It is a special closure.

2. Nested functions

Nested functions are closures that have a name and can capture values from their enclosing function. 

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func makeIncrementer() -> () -> Int {
    var runningTotal = 10
    // nested function，it is a closure too.
    func incrementer() -> Int{
        runningTotal += 1
        return runningTotal
    }
    return incrementer
}

3. Closure expressions

Closure expressions are unnamed closures written in a lightweight syntax that can capture values from their surrounding context.

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{ (param) -> ReturnType in
    // Method body
}

Swift’s closure expressions have a clean, clear style, with optimizations that encourage brief, clutter-free syntax in common scenarios. These optimizations include:

  1. Inferring parameter and return value types from context
  2. Implicit returns from single-expression closures
  3. Shorthand argument names
  4. Trailing closure syntax

Reference

https://docs.swift.org/swift-book/LanguageGuide/Closures.html