Question

无法在swift中viewDidLoad()重载功能。它给出了错误definition conflict with previous value" at "func joinString(#strings: String...) -> String {

override func viewDidLoad() {
    super.viewDidLoad()
    func joinString(#strings: String[]) -> String {
            var str = "" 
            for s in strings {
                str += s
            }
            return str
        }
    func joinString(#strings: String...) -> String {
            return joinString(strings: strings)
        }
    println(joinString(strings : ["I", "am", "an", "array"]))
    println(joinString(strings : "I", "am", "an", "array"))
}

Answer 1

对我来说，这看起来像是一个Swift bug（或一个没有文档的限制）。函数/方法重载通常工作，即使是数组与可变参数：

class MyClass {

    func foo(arg: Int) { println("An integer") }
    func foo(arg: Double) { println("A double") }

    func joinString(#strings: String[])  { println("An array") }
    func joinString(#strings: String...)  { println("Variadic parameters")}

    func test() {
        foo(2)
        foo(3.14)
        joinString(strings : ["I", "am", "an", "array"])
        joinString(strings : "I", "am", "an", "array")
    }
}

并产生预期的输出：

An integer
A double
An array
Variadic parameters

但是重载不适用于嵌套函数：

class MyClass {

    func test() {

        func foo(arg: Int) { println("An integer") }
        func foo(arg: Double) { println("A double") }
        // error: definition conflicts with previous value

        func joinString(#strings: String[])  { println("An array") }
        func joinString(#strings: String...)  { println("Variadic parameters")}
        // error: definition conflicts with previous value

        func test() {
            foo(2)
            foo(3.14)
            joinString(strings : ["I", "am", "an", "array"])
            joinString(strings : "I", "am", "an", "array")
        }
    }
}

Answer 2

你不能以这种方式超载：

func joinString(#strings: String[]) -> String {
 ...
}
func joinString(#strings: String...) -> String {
    ...
}

joinString函数实际上具有相同的签名。两者都采用Array但可变版本的签名会导致编译器使用调用站点传递的参数生成Array。

无法在swift中的viewDidLoad（）中重载函数

2 个答案: