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复杂类型的Swift CustomStrings敞篷车

swift

stevenpcurtis · 技术社区 · 7 年前

我希望CustomStringConvertible为我提供节点的描述,特别是它包含的边。

作为背景,我一直在研究图论,并创建了一个节点:

class Node : CustomStringConvertible {
    // unique identifier required for each node
    var identifier : Int
    var distance : Int = Int.max
    var edges = [Edge]()
    var visited = false

    var description: String {
        return "identifier: " + identifier.description + ", Edges: " + ( "edgesString" )
    }

    init(visited: Bool, identifier: Int, edges: [Edge]) {
        self.visited = visited
        self.identifier = identifier
        self.edges = edges
    }

    static func == (lhs: Node, rhs: Node) -> Bool {
        return lhs.identifier == rhs.identifier
    }
}

有棱角

class Edge {
    var from: Node // does not actually need to be stored!
    var to: Node
    var weight: Int
    var description : String {
        return "from: " + from.description + ", to: " + to.description + ", weight: " + weight.description
    }
    init(to: Node, from: Node, weight: Int) {
        self.to = to
        self.weight = weight
        self.from = from
    }
}

我可以很容易地打印出每个节点的每个边

testGraph.nodes.forEach{$0.edges.forEach{print($0.description)}

我试着为每一个语句写下与我的相同的内容

var description: String {
    var edgesString = String()
    edges.forEach{  edgesString.append($0.description)}
    return "identifier: " + identifier.description + ", Edges: " + ( edgesString )
}

但是执行提供了一个EXC_BAD_访问在这种情况下,事实上我无法得到任何代码来完成,并给我节点和其中包含的边的描述。

如何完成节点的描述字符串,然后继续描述边?

1 回复 | 直到 7 年前

taka 7 年前

看来你的 description Node.description Edge.description .

Node 呼叫 边缘描述 对于每个边,以及 Edge 呼叫 Node.description 用于其“从”和“到”节点。如果图具有圆形连接,而不是星形连接,则会导致无限roop。

一个简单的方法是唯一显示 Node.identifier 而不是详细的描述。

class Edge {
    var from: Node // does not actually need to be stored!
    var to: Node
    var weight: Int
    var description : String {
        return "{ Edge, from: \(from.identifier), to: \(to.identifier), weight: \(weight) }"
    }
    init(to: Node, from: Node, weight: Int) {
        self.to = to
        self.weight = weight
        self.from = from
    }
}
class Node : CustomStringConvertible {
    // unique identifier required for each node
    var identifier : Int
    var distance : Int = Int.max
    var edges = [Edge]()
    var visited = false

    var description: String {
        let edgesString = edges.map { $0.description }.joined(separator: ", ")
        return "{ Node, identifier: \(identifier), Edges: [\(edgesString)] }"
    }

    init(visited: Bool, identifier: Int, edges: [Edge]) {
        self.visited = visited
        self.identifier = identifier
        self.edges = edges
    }

    static func == (lhs: Node, rhs: Node) -> Bool {
        return lhs.identifier == rhs.identifier
    }
}

let rootNode = Node(visited: false, identifier: 10, edges: [])
var edges: [Edge] = []
for i in 0..<3 {
    let node = Node(visited: false, identifier: i, edges: [])
    let edge = Edge(to: node, from: rootNode, weight: i)
    edges.append(edge)
}
rootNode.edges = edges

print(rootNode)
// { Node, identifier: 10, Edges: [{ Edge, from: 10, to: 0, weight: 0 }, { Edge, from: 10, to: 1, weight: 1 }, { Edge, from: 10, to: 2, weight: 2 }] }

visited 成员),并尝试不访问那些已访问的节点。