从符合者数组创建@objc 协议类型数组

Question

我尝试了很多方法来做到这一点，但 swift 编译器会抱怨我所做的一切。 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。我在撕头发。

我正在尝试为 table 视图内容构建一个简单的数组。 "rows" 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，那些类符合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 "works" （即不会在运行时崩溃）但我似乎在我的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
}

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
}

我只想把我的 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，因为感觉我已经以各种可能的方式重写了这些循环。

我错过了什么？为什么我似乎不能成功迭代而不是重复所有这些代码？

更新

这就是戴维斯代码所发生的事情：

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（我从变量视图中打印了 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 = {}

是我一个人还是这些数字加起来不合？

Answer 1

生成一堆此处缺失的代码后，我想出了以下似乎可以按您预期工作的代码：

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 { [=10=]?.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: [=10=]!) }

请注意，这使用了几个非常重要的内置函数 filter 和 map 我建议您真正深入研究它们，而且 reduce 是非常强大的内置函数这几乎消除了手动进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({ [=11=]?.count > 0 })
                                            .map({ (sectionTitle:"test", rows: [=11=]!) })

从符合者数组创建@objc 协议类型数组

Creating an array of @objc protocol type from arrays of conformers

arrays

protocols

swift

swift-protocols