ios - Swift 2.0 元组模式元素标签必须是 '_'

Question

自 swift 2.0 更新以来，我一直在尝试修复我的所有代码。我有一个问题，似乎是元组现在的工作方式:

public func generate() -> AnyGenerator <(String, JSON)> {
    switch self.type {
    case .Array:
        let array_ = object as! [AnyObject]
        var generate_ = array_.generate()
        var index_: Int = 0
        return anyGenerator{
            if let element_: AnyObject = generate_.next() {
                return ("\(index_++)", JSON(element_))
            } else {
                return nil
            }
        }
    case .Dictionary:
        let dictionary_ = object as! [String : AnyObject]
        var generate_ = dictionary_.generate()
        return anyGenerator{
            if let (key_: String, value_: AnyObject) = generate_.next() {
                return (key_, JSON(value_))
            } else {
                return nil
            }
        }
    default:
        return anyGenerator{
            return nil
        }
    }
}

特别是行:

if let (key_: String, value_: AnyObject) = generate_.next()

正在抛出错误:元组模式元素标签'key'必须是'_'

我已经尝试过进行更改，但没有成功...

有什么想法吗？

Answer 1

问题是:我们不能在元组模式内部使用类型注释。

在release notes :

Type annotations are no longer allowed in patterns and are considered part of the outlying declaration. This means that code previously written as:

var (a : Int, b : Float) = foo()

needs to be written as:

var (a,b) : (Int, Float) = foo()

if an explicit type annotation is needed. The former syntax was ambiguous with tuple element labels. (20167393)

所以，你可以:

if let (key_, value_): (String, AnyObject) = generate_.next() {

但在这种情况下，您可以省略 : (String, AnyObject):

if let (key_, value_) = generate_.next() {