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protocol JSONParser {
    static func obtainModel(from json: JSON) -> Self?
}

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// Some model
struct MyModel {
    let name: String
    let number: Int
    let date: NSDate
}

// Conforming to the new protocol
extension MyModel: JSONParser {
    static func obtainModel(from json: JSON) -> MyModel? {

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let json = JSON(data: dataFromServer)

if let model = MyModel.obtainModel(from: json) {
    // success
} else {
    // failure
}

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struct Node {
    let name: String
    var visited: Bool = false
    var connections: [Connection] = []
  
    init(name: String) {
        self.name = name
    }
}

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struct Connection {
    let to: Node
    let weight: Int
  
    init(to toNode: Node, weight: Int) {
        assert(weight >= 0, "connection weight has to be equal or greater than zero")
    
        self.to = toNode
        self.weight = weight
    }

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struct Path {
    let cumulativeWeight: Int
    let lastNode: Node
    let previousPath: Path?
}

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init(toNode: Node, viaConnection: Connection?=nil, viaPath: Path?=nil) {
    if let
        previousPath = viaPath,
        lastConnection = viaConnection {
            self.cumulativeWeight = lastConnection.weight + previousPath.cumulativeWeight
    } else {
        self.cumulativeWeight = 0
    }
    
    self.lastNode = toNode

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func ==(x: Path, y: Path) -> Bool {
    return x.cumulativeWeight == y.cumulativeWeight
}

func <(x: Path, y: Path) -> Bool {
    return x.cumulativeWeight < y.cumulativeWeight
}

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struct Path: Comparable {
    let cumulativeWeight: Int
    let lastNode: Node
    let previousPath: Path?
  
    init(toNode: Node, viaConnection: Connection?=nil, viaPath: Path?=nil) {
        if let
            previousPath = viaPath,
            lastConnection = viaConnection {
                self.cumulativeWeight = lastConnection.weight + previousPath.cumulativeWeight

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internal func shortestPath(source: Vertex, destination: Vertex) -> Path? {
    var frontier: [Path] = [] {
        didSet {
            frontier.sortInPlace()
        }
    }
    
    var finalPaths: [Path] = [] {
        didSet {
            finalPaths.sortInPlace()