In an array containing objects, changing one item's property doesn't change the object itself

Question

This will not happen if I just change the properties instead of replacing the reference to a new object.

Here is a class Person, which is a reference type,

class Person {
    var firstName: String
    var lastName: String
    init(firstName: String, lastName: String) {
        self.firstName = firstName
        self.lastName = lastName
    }
}

Here is an instance of Person,

var someone = Person(firstName: "Johnny", lastName: "Appleseed")

then I make an array containing values of type Person

var lotsOfPeople = [someone, someone, someone]

I suppose lotsOfPeople containing 3 references to someone. But if I change the third value in lotsOfPeople,

lotsOfPeople[2] = Person(firstName: "Lucy", lastName: "Swift")

someone itself isn't changed.

print(someone.firstName) // Johnny

I think it means lotsOfPeople[2] is not a reference to someone. How could this happen?

rmaddy · Accepted Answer · 2019-03-20 16:18:02Z

4

The problem is that you are replacing the reference at lotsOfPeople[2] to point to a new object. That is why the original Person is not changed.

If you did lotsOfPeople[2].firstName = "Lucy" then it would change.

Or do:

let person = lotsOfPeople[2]
person.firstName = "Lucy"

then you would also see the original change.

answered Mar 20, 2019 at 16:18

rmaddy

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