我尝试通过继承两个类来创建myPet，但是出现错误，例如：

import UIKit
class SecondViewController: UIViewController, UITextFieldDelegate {
    // No Error
}

然后定义了以下类，然后创建新的类myPets，我想同时继承Dog和Substance。但是错误：从类“狗”和“物质”的多重继承

class Dog:Animal {
    func sound()->String {
        return "Hong Hong"
    }
}

class Substance {
    func livingCompound()->String {
        return "Consist of bio-molecule"
    }
}

class myPets:Dog, Substance {
    func itsAddress()->String {
        // Error:Multiple inheritance from classes 'Dog' and 'Substance'
    }
}