从一致性数组创建一个 @objc 协议类型数组

Question

我尝试了很多方法，但无论我做什么，快速编译器都会抱怨。 SourceKit 和编译器也不停地崩溃，所以我什至不能再试验了。甚至不插入一些printlns。我在扯头发。

我正在尝试为表格视图内容构建一个简单的数组。 “行”是Presentable 对象，它只是协议的集合。

import Foundation

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

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）

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

2。这个“有效”（即在运行时不会崩溃）但我的新数组中似乎没有对象：

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
}

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
}

我想要的只是把我的buses, metros, trains, trams, ships 放在一个[Presentable] 中，没有代码墙。我开始相信这在 Swift 中是不可能的，因为感觉就像我以各种可能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？

---

更新

这就是 Davids 代码发生的情况：

与上面相同的控制台输出，但这次它在尝试访问 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（我从变量视图打印了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，还是这些数字不加起来？

Answer 1

在生成了这里缺少的一堆代码后，我想出了以下内容，似乎可以按您的预期工作：

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，这使用了两个非常重要的内置函数 filter 和 map 我建议深入研究它们，因为它们加上 reduce 是非常强大的内置函数，几乎无需手动操作做你自己的数组迭代。

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!) })