如何对带有选项的数组执行索引?

In Swift2, how can you do indexOf on arrays that contain optionals? The following example won't compile:

在Swift2中，如何在包含选项的数组上执行indexOf ?下面的示例无法编译:

var strings: [String?] = ["hello", nil, "world"]
let index = strings.indexOf("world")

with the compiler complaining

与编译器抱怨

"Cannot invoke indexOf with an argument list of type '(String)'"

"不能使用'(String)' '类型的参数列表调用indexOf "

A naive approach without indexOf would be:

没有索引的幼稚方法是:

let index: Int = {
    for var i = 0; i < strings.count; i++ {
        let s: String? = strings[i]
        if s == "world" {
            return i
        }
    }
    return -1
}()

Isn't there any way to use the built-in indexOf function?

难道没有办法使用内置的indexOf函数吗?

The same example however works for arrays with non-optionals:

同样的例子也适用于非选项数组:

var strings: [String] = ["hello", "world"]
let index = str.indexOf("world")

2 个解决方案

#1

Or even simpler:

或者更简单:

let strings: [String?] = ["hello", nil, "world"]
strings.indexOf{ $0 == "world" }

This works because == is defined for optionals as well

这是有效的，因为=也是为选项定义的

#2

You can use an expression in "trailing closure" for indexOf:

你可以在indexOf中使用“尾闭包”中的表达式:

var arr: [String?] = ["hello", nil, "world"]
let i = arr.indexOf() { $0 != nil && $0 == "world" }

#1