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func restURL<T:RestResource>(r:T) -> String {
    return "/\(T.restName())/\(r.restId())"
}

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protocol RestResource {
    static func restName() -> String
    func restId() -> String
}

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struct Customer {
    var identifier:Int = 0
}

struct Product {
    var identifier:Int = 0
}

struct Order {
    var identifier:Int = 0

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protocol Identifiable {
    var identifier:Int {get}
}

struct Customer:Identifiable {
    var identifier:Int = 0
}

struct Product:Identifiable {
    var identifier:Int = 0

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extension RestResource where Self:Identifiable {
    func restId() -> String { return "\(identifier)" }
}

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extension Customer:RestResource {   static func restName() -> String { return "customers" } }
extension Product:RestResource {    static func restName() -> String { return "products" } }
extension Order:RestResource {      static func restName() -> String { return "orders" } }

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let customer = Customer(identifier: 1234)
restURL(customer) // -> "/customers/1234"

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let customer = Customer(identifier: 1234)
// We want to generate "/customers/1234"

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extension Customer:RestResource {
    
    static func restName() -> String {
        return "customers"
    }
    
    func restId() -> String {
        return "\(identifier)"
    }
}

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typealias JSON = AnyObject

protocol JSONParsable {
    init(json: JSON)
}