arrays - 从符合者数组创建 @objc 协议(protocol)类型数组

Question

我尝试了很多方法来做到这一点，但无论我做什么，快速编译器都会提示。 SourceKit和编译器也不停地崩溃，所以我什至无法再进行实验了。甚至不插入一些println s。我正在撕扯我的头发。

我正在尝试为 TableView 内容构建一个简单的数组。 “行”是 Presentable对象，它只是协议(protocol)的集合。

import Foundation

// The protocols are all @objc
typealias Presentable = protocol<Utterable, Displayable, Departure>
typealias TableSection = (sectionTitle: String, rows: [Presentable])

<强>1。这不起作用:

( buses, metros 等都是 [Bus]?, [Metro]? 等，并且这些类符合 Presentable 的所有协议(protocol))

private func asContent5() -> [TableSection]
{
    var result: Array<TableSection> = []

    var deptsCollections: [[Presentable]?] = [ buses, metros, trains, trams, ships ]
    for var i = 0; i<deptsCollections.count ; i++ {
        if let departures = deptsCollections[i]? {
            var newDeparturesArray: [Presentable] = []
            for dep in departures
            {
                newDeparturesArray.append(dep) // EXC_BAD_INSTRUCTION
            }
            let tuple: TableSection = (sectionTitle: "test", rows: newDeparturesArray)
            result.append(tuple)
        }
    }
    return result
}

控制台输出:

fatal error: NSArray element failed to match the Swift Array Element type

<强>2。这“有效”(即在运行时不会崩溃)，但我似乎在新数组中没有得到任何对象:

private func asContent4() -> [TableSection]
{
    var result: Array<TableSection> = []

    var deptsCollections: [AnyObject?] = [ buses, metros, trains, trams, ships ]
    for var i = 0; i<deptsCollections.count ; i++ {
        if let departures: [Presentable] = deptsCollections[i] as? [Presentable] {
            var newDeparturesArray: [Presentable] = []
            for dep in departures
            {
                newDeparturesArray.append(dep as Presentable)
            }
            let tuple: TableSection = (sectionTitle: "test", rows: newDeparturesArray)
            result.append(tuple)
        }
    }
    return result
}

<强>3。这完全有效:

private func asContent3() -> [TableSection]
{
    var result: Array<TableSection> = []

    if let departures = buses {
        var newDeparturesArray: [Presentable] = []
        for dep in departures { newDeparturesArray.append(dep as Presentable) }
        let tuple: TableSection = (sectionTitle: "bus", rows: newDeparturesArray)
        result.append(tuple)
    }

    if let departures = metros {
        var newDeparturesArray: [Presentable] = []
        for dep in departures { newDeparturesArray.append(dep as Presentable) }
        let tuple: TableSection = (sectionTitle: "metro", rows: newDeparturesArray)
        result.append(tuple)
    }

    if let departures = trains {
        var newDeparturesArray: [Presentable] = []
        for dep in departures { newDeparturesArray.append(dep as Presentable) }
        let tuple: TableSection = (sectionTitle: "trains", rows: newDeparturesArray)
        result.append(tuple)
    }

    if let departures = trams {
        var newDeparturesArray: [Presentable] = []
        for dep in departures { newDeparturesArray.append(dep as Presentable) }
        let tuple: TableSection = (sectionTitle: "trams", rows: newDeparturesArray)
        result.append(tuple)
    }

    if let departures = ships {
        var newDeparturesArray: [Presentable] = []
        for dep in departures { newDeparturesArray.append(dep as Presentable) }
        let tuple: TableSection = (sectionTitle: "ships", rows: newDeparturesArray)
        result.append(tuple)
    }

    return result
}

我想要的就是拿走我的 buses, metros, trains, trams, ships并将它们放入 [Presentable]每个，没有代码墙。我开始相信这在 Swift 中是不可能的，因为感觉就像我已经以各种可以想象的方式重写了这些循环。

我错过了什么？为什么我似乎无法成功迭代而不是重复所有这些代码？

<小时/>

更新

这就是 Davids 代码所发生的情况:

与上面相同的控制台输出，但是这次在尝试访问 TableSection::rows 时崩溃(我以前也发生过这种情况)。这使它崩溃:

println("index path s: \(indexPath.section) r: \(indexPath.row)")
let section = tableContent[indexPath.section]
println("row count: \(section.rows.count)")
let departure: Presentable = section.rows[indexPath.row] // crash

控制台(我从变量 View 打印了 rows 数组):

index path s: 0 r: 0
row count: 8
fatal error: NSArray element failed to match the Swift Array Element type
Printing description of section.rows:
([protocol<Departure, Displayable, Utterable>]) rows = {}

只有我一个人这么认为还是这些数字加起来不对？

Answer 1

生成一堆此处缺少的代码后，我想出了以下似乎可以按您的预期工作的代码:

import Foundation

@objc protocol Utterable {}
@objc protocol Displayable {}
@objc protocol Departure {}

typealias Presentable = protocol<Utterable, Displayable, Departure>
typealias TableSection = (sectionTitle: String, rows: [Presentable])

class Bus : Presentable {}
class Metro : Presentable {}
class Train : Presentable {}
class Tram : Presentable {}
class Ship : Presentable {}

let buses : [Bus]? = nil
let metros : [Metro]? = [ Metro() ]
let trains : [Train]? = [ Train() ]
let trams : [Tram]? = nil
let ships : [Ship]? = [Ship()]

let departments : [[Presentable]?] = [ buses, metros, trains, trams, ships]

// filter out the non-nil departments that actually have elements
let acceptable = departments.filter { $0?.count > 0 }

// map the acceptable departments into sections, note that we force-unwrap
//  dept because we already verified in the step above that it must be
//  valid
let sections : [TableSection] = acceptable.map { (sectionTitle:"test", rows: $0!) }

请注意，这使用了几个非常重要的内置函数 filter 和 map 我建议真正深入研究它们，再加上 reduce > 是非常强大的内置函数，几乎消除了手动执行自己的数组迭代的需要。

或者，为了紧凑，您可以使用:

// or for compactness...
let sections2 : [TableSection] = departments.filter({ $0?.count > 0 })
                                            .map({ (sectionTitle:"test", rows: $0!) })