Array of functions in Swift

问题

How can I store an array of functions to callback later in an array like in JavaScript? Any and AnyObject type cannot hold functions with different types of method signatures.

回答1:

You can use an enum to put various functions into the Array and then extract the functions with a switch.

    enum MyFuncs {
        case Arity0 ( Void -> Void )
        case Arity2 ( (Int, String) -> Void)
    }

    func someFunc(n:Int, S:String) { }
    func boringFunc() {}
    var funcs = Array<MyFuncs>()
    funcs.append(MyFuncs.Arity0(boringFunc))
    funcs.append( MyFuncs.Arity2(someFunc))

    for f in funcs {
        switch f {
        case let .Arity0(f):
            f()  // call the function with no arguments
        case let .Arity2(f):
            f(2,"fred") // call the function with two args
        }
    }

回答2:

Note: this answer is for Swift versions 1.0 and lower.

Functions that have different parameters and return types are of a different type so they can't be stored in an array together. They also don't conform to the Any or AnyObject protocols.

If you have functions with the same parameters though you can work around that. Even though the functions below return a tuple of Double and an Int, they can both be defined as () -> Any function types.

func func1 () -> Int {
    return 1
}
func func2 () -> (Double, Double){
    return (2, 3)
}
var a: () -> Int = func1
var b: () -> (Double, Double) = func2

var arr: Array< () -> Any> = [a, b]

回答3:

Below is an example with both an array and a dictionary. Tested and working in Xcode 6.1 (6A1046a). Note that functions from dictionaries must first be unwrapped.

This technique does however fall apart when the functions have different parameter or return types, for the reasons explained by connor in his answer.

class MyViewController: UIViewController
{
    let arrayOfFunctions = [function1, function2]

    let dictionaryOfFunctions = [
        "function1": function1,
        "function2": function2
    ]

    func function1() {
        NSLog("function1")
    }

    func function2() {
        NSLog("function2")
    }

    override func viewDidLoad()
    {
        let fn1 = arrayOfFunctions[0]
        fn1(self)()

        let fn2 = dictionaryOfFunctions["function2"]
        fn2!(self)()
    }
}

回答4:

As of Swift 1.1, all function types conform to Any, so you can hold functions in an Any array.

func foo (str: String) -> Int {
    return 1
}
func bar () -> (Double, Double){
    return (2, 3)
}
var a: Any = foo
var b: Any = bar

var arr: Any = [a, b]

来源：https://stackoverflow.com/questions/24418951/array-of-functions-in-swift

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swift

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