swift 相当于 "?:"

Question

ObjC

[MyObject doThisWithString:string?: [MyObject otherString]];

我如何在 Swift 中执行此操作？

extension MyObject {
    func doThisWithString(string: String?) {
        ... <- assume defined
    }

    func otherString() -> String {
        return ... <- assume defined
    }
}

var MyInstance: MyObject
...
MyInstance.doThisWithString(myStringVar?: MyInstance.otherString()) <- how do I do this?

Answer 1

有一个'??'称为“Nil 合并”运算符的运算符。它做的正是你需要的。引用documentation :

Nil Coalescing Operator

The nil coalescing operator (a ?? b) unwraps an optional a if it contains a value, or returns a default value b if a is nil. The expression a is always of an optional type. The expression b must match the type that is stored inside a.

The nil coalescing operator is shorthand for the code below:

a != nil ? a! : b

在您的情况下，您可以将表达式写为:

MyInstance.doThisWithString(myStringVar ?? MyInstance.otherString())