Swift泛型：非名义类型不支持显式初始化 [英] Swift generics: Non-nominal type does not support explicit initialization

问题描述

所以我想了解泛型协议和类：

  protocol ListPresenterType where View.PDO.SW == Dispatcher .SW {
 associatedtype Dispatcher：ListDispatcherType 
 associatedtype View：ListViewType 
 
 init（调度程序：调度程序，状态：@escaping（_ state：AppState） - >（ListState< Dispatcher .SW>））
 
 func attachView（_ view：View）
 ... 
} 
  

我从另一个泛型类开始：

pre $ class $ AbstractListViewController<演示者：ListPresenterType，PDO：ListPDOCommonType，...>：ListViewType，...其中PDO.SW == Presenter.Dispatcher.SW，... {
func configure（withBla：bla）{
...
presenter = Presenter（dispatcher：dispatcher，state：state）
}

func someFunc（）{
presenter.attachView（self）//错误：无法用类型的参数列表调用'attachView'。 ..
}

据我所知，我试图初始化符合一个通用的协议，它工作得很好，但视图类型必须与我试图在 attachView（：）中提供它的内容不一致。

然后我试着用具体的视图初始化它，改变 init ：

<$ （Dispatcher：Dispatcher，view：View，state：@escaping（_ state：AppState） - >（ListState< Dispatcher.SW>））{
self.view = view
...
}

并且在 AbstractListViewController ：

  presenter = Presenter（dispatcher：dispatcher，view：self，state：state） 
  

获得这个臭名昭着的错误：

非名义类型'Presenter'不支持显式初始化
  

这里有相关游乐场的要点：

成功的init（尽管不能调用 attachView（：）） https://gist.github.com/nikans/0fde838846ffa9ff2da48c923f850625

1. 初始化失败，出现上述错误： https://gist.github.com/nikans/53c3ea146ceb12dc8461f7ba8a81793d
   

请注意，每个空白协议实际上都是一个通用协议，我刚刚删除了不必要的细节。

---

我想了解：

1. 是什么让突然出现的名义类型非名义令人惊讶的是，它是一个符合通用协议的泛型参数，但我不明白这个因果关系。）


2. 我听说过类型擦除的一些事情，但是如果它是适用于此。

谢谢。

解决方案

）错误，如非名义类型'％type'不支持显式初始化简单地等于不匹配类型错误少于错误的Xcode（如果这是一件事情）：不能用'...'类型的参数列表调用类型为'％'的初始值设定项，期望类型为'...'的参数列表

So I'm trying to understand generic protocols and classes:

protocol ListPresenterType where View.PDO.SW == Dispatcher.SW {
    associatedtype Dispatcher: ListDispatcherType
    associatedtype View: ListViewType

    init(dispatcher: Dispatcher, state: @escaping (_ state: AppState)->(ListState<Dispatcher.SW>))

    func attachView(_ view: View)
    ...
}

And I'm initiating it from another generic class:

class AbstractListViewController<Presenter: ListPresenterType, PDO: ListPDOCommonType, ...>: ListViewType, ... where PDO.SW == Presenter.Dispatcher.SW, ... {
    func configure(withBla: bla) {
        ...
        presenter = Presenter(dispatcher: dispatcher, state: state)
    }

    func someFunc() {
        presenter.attachView(self) // ERROR: Cannot invoke 'attachView' with an argument list of type ...
}

As I understand, I'm trying to initialize a type conforming to a generic protocol, which works just fine, but the type of View must be inconsistent with what I'm trying to feed it in attachView(:).

Then I try to initialize it with concrete view, changing init:

init(dispatcher: Dispatcher, view: View, state: @escaping (_ state: AppState)->(ListState<Dispatcher.SW>)) { 
    self.view = view 
    ... 
}

And in AbstractListViewController:

presenter = Presenter(dispatcher: dispatcher, view: self, state: state)

And getting this infamous error:

Non-nominal type 'Presenter' does not support explicit initialization

Here're gists with relevant playgrounds:

1. Successful init (though cannot invoke attachView(:)) https://gist.github.com/nikans/0fde838846ffa9ff2da48c923f850625
2. Init failing with aforementioned error: https://gist.github.com/nikans/53c3ea146ceb12dc8461f7ba8a81793d

Please notice that every empty protocol there is in fact a generic protocol, I've just removed the unnecessary details.

---

I'd like to understand:

1. What makes a "nominal" type "non-nominal" all of a sudden (nothing to be surprised of, it's a generic parameter conforming to a generic protocol, but I don't understand the causation).
2. I heard something about type erasure, but didn't quite get if it is applicable here.

Thanks.

解决方案

So it appears that in Xcode9 (beta 6) errors like Non-nominal type '%type' does not support explicit initialization simply equals the mismatching types error in less buggy Xcode (if that's a thing): cannot invoke initializer for type '%type' with an argument list of type '...' expected an argument list of type '...'

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