具有通用项目的Swift数组扩展 [英] Swift Array extension with generic items

问题描述

  struct Section< InfoT：Equatable，ItemsT：Equatable> {
让info：InfoT？ 
 let items：[ItemsT] 
} 
  

这个泛型类型元素的方法：

 扩展数组元素==部分< Equatable，Equatable> {
 //只是虚拟示例函数：
 func debugDummy（）{
 for self {
 let info = section.info $ b $ print（section info： \（info）。）
 for section in section.items {
 print（item：\（item）。）
} 
} 
 } 
} 
  

这给我编译错误：

 错误：不支持'Equatable'作为符合协议'Equatable'的具体类型
扩展数组其中Element == Section  ^ 
 
错误：GenericsListPlayground.playground：6：24：错误：'Element'类型的值没有成员'info'
 let info = section.info 
 ^ ~~~~~~ ~~~~ 
 
错误：GenericsListPlayground.playground：8：25：error：类型'Element'的值没有成员'items'
 for item in section.items {
 ^ ~~~~~~ ~~~~~ 
  

如何正确声明这样的扩展名？我已经尝试了几个声明这个扩展的变体，比如：

 扩展数组元素==部分（无参数）$ b $ 
 
 
 
 错误：对泛型类型'Section'的引用需要< ...>中的参数。 
  
 etc ...他们都不想编译。
 
 
 
  import Foundation 
 $ b解决方案

$ b协议Section {
associatedtype InfoT：可衡量
相关类型ItemsT：可衡量
var info：InfoT？ {get}
var items：[ItemsT] {get}
}

扩展数组元素：部分{
//虚拟示例函数：
func debugDummy（）{
for section in self {
let info = section.info
print（section info：\（String（describe：info））。）
$为b中的项目{b $ b print（item：\（item）。）
}
}
}
}


I am using Swift 3.1 and have some generic struct:

struct Section<InfoT: Equatable, ItemsT: Equatable> {
    let info: InfoT?
    let items: [ItemsT]
}

And want array extension with custom method for elements of this generic type:

extension Array where Element == Section<Equatable, Equatable> {
    // Just dummy example function:
    func debugDummy() {
        for section in self {
            let info = section.info
            print("section info: \(info).")
            for item in section.items {
                print("item: \(item).")
            }
        }
    }
}

This gives me compilation errors:

error: using 'Equatable' as a concrete type conforming to protocol 'Equatable' is not supported
extension Array where Element == Section<Equatable, Equatable> {
                                 ^

error: GenericsListPlayground.playground:6:24: error: value of type 'Element' has no member 'info'
            let info = section.info
                       ^~~~~~~ ~~~~

error: GenericsListPlayground.playground:8:25: error: value of type 'Element' has no member 'items'
            for item in section.items {
                        ^~~~~~~ ~~~~~

How to properly declare such extension? I have tried few variations for declaring this extension, like:

extension Array where Element == Section (no arguments)

produces:

error: reference to generic type 'Section' requires arguments in <...>

etc... none of them want to compile.

解决方案

Try this:

import Foundation

protocol Section {
    associatedtype InfoT: Equatable
    associatedtype ItemsT: Equatable
    var info: InfoT? { get }
    var items: [ItemsT] { get }
}

extension Array where Element: Section {
    // Just dummy example function:
    func debugDummy() {
        for section in self {
            let info = section.info
            print("section info: \(String(describing: info)).")
            for item in section.items {
                print("item: \(item).")
            }
        }
    }
}

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