Swift 3需要更多信息来推断参数？ [英] Swift 3 needs more info, to infer a parameter?

问题描述

我有一个向上冒泡的扩展，

但在Swift 3中，

通用参数'T'无法推断

 公共扩展UIResponder 
 {
 public func next< T>（） - > T' 
 {
 guard let responder = self.next 
 else {return nil} 
 return（responder as？T）?? responder.next（）
} 
} 
 
 //注意 - 对这个优秀帖子的赞誉：
 // https://blog.veloxdb.com/2016 / 05/12 / bubbling-events-using-uiresponder-in-swift / 
  

在Swift中<3 ，你可以像这样使用它：

  class SnapDot：UIView 
 {
 ..... 
 func handleTap（g：UITapGestureRecognizer）
 {
（next（）as Snap？）?. oneDotWasClicked（self）
} 
  

恐怕不仅（a）我不明白为什么它不会在Swift 3中被推断，但是（b）无休止地尝试随机变化，我无法让它在Swift 3中工作：O

解决方案

现有下一步 UIResponder 的方法以及您的扩展方法。 self.next 在$ b $内部，您的方法引用（generic）方法本身。

重命名扩展名使它编译：

  public extension UIResponder {
 public func nextOfType< T>（） - > T' {
 guard let responder = self.next 
 else {return nil} 
 return（responder as？T）?? responder.nextOfType（）
} 
} 
  

即使你没有' t请求它，这是一个迭代，而不是
递归版本：）

pre $ code> public extension UIResponder {
public func nextOfType< T>（） - > T' {
var current = self
let responder = current.next {
if let match = responder as？ T {
return match
}
current = responder
}
return nil
}
}

I have an extension which bubbles upwards,

but in Swift 3,

Generic parameter 'T' could not be inferred

public extension UIResponder
    {
    public func next<T>() -> T?
        {
        guard let responder = self.next
            else { return nil }
        return (responder as? T) ?? responder.next()
        }
    }

 // note - kudos to this excellent post:
 // https://blog.veloxdb.com/2016/05/12/bubbling-events-using-uiresponder-in-swift/

in Swift<3, you could use that like this:

class SnapDot:UIView 
    {
    .....
    func handleTap(g:UITapGestureRecognizer)
        {
        (next() as Snap?)?.oneDotWasClicked(self)
        }

I'm afraid that not only (a) I can't see why it wouldn't be inferred in Swift 3, but (b) even by endlessly trying random variations, I can't get it to work in Swift 3 :O

解决方案

That is a name collision between the existing next method of UIResponder, and your extension method. self.next inside your method refers to the (generic) method itself.

Renaming the extension makes it compile:

public extension UIResponder {
    public func nextOfType<T>() -> T? {
        guard let responder = self.next
            else { return nil }
        return (responder as? T) ?? responder.nextOfType()
    }
}

And even if you didn't ask for it, here is an iterative instead of recursive version :)

public extension UIResponder {
    public func nextOfType<T>() -> T? {
        var current = self
        while let responder = current.next {
            if let match = responder as? T {
                return match
            }
            current = responder
        }
        return nil
    }
}

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