Class vs Struct

The main difference between classes and structs are that structs are value types and so values are copied over, while classes are reference types. Classes also have inheritance, so you can have subclasses that have the same methods and variables as their superclass.

When you assign the value of one struct to another, it actually copies the data. In the code below, you'll see MyStruct has a variable "a". I assign this to firstStruct and give it the value "Stuff", and then copy it to secondStruct. I then change the firstStruct.a to "New Stuff", but secondStruct.a stays as "Stuff".

This is not the same as the class. Notice when I do the same thing, when I change firstClass.a to "New Stuff", secondClass.a changes as well.

As far as the class, you need to explicitly state what the init method is, unless you only have optionals.

Try copying the code below into a playground to see how it works.

struct MyStruct {
    var a: String
}

var firstStruct = MyStruct(a: "Stuff")

var secondStruct = firstStruct

secondStruct.a
// "Stuff"

firstStruct.a = "New Stuff"

secondStruct.a
// "Stuff"

class MyClass {
    var a: String

    init(a: String) {
        self.a = a
    }
}

var firstClass = MyClass(a: "Stuff")

var secondClass = firstClass

secondClass.a
// "Stuff"

firstClass.a = "New Stuff"

secondClass.a
// "New Stuff"