class.swift

class Dog {
    var name: String
    var weight: Int

    // constructor or initializer
    init(name: String, weight: Int) {
        self.name = name                  
        self.weight = weight
    }
}

var myDog = Dog(name: "Ranger", weight: 10)
var yourDog = myDog     // reference copy
yourDog.name = "Puncher"
print(myDog.name)       // "Puncher"
print(yourDog.name)     // "Puncher"