Can a struct in swift have a copy constructor

Question

I have a struct and a class:

class FooClass {
    var someValue: String = "123"
}
struct TestStruct {
    var aValue: Int = 12
    var clsValue: FooClass
}

And I want a deep copy for TestStruct, but the following code will also change clsValue in variable a:

var a = TestStruct(aValue: 10, clsValue: FooClass())
var b = a
b.clsValue.someValue = "abc"

I know the class value in the struct is copied only 'reference', but I want a deep copy for this class when I assigning a to b.

I do know c++ can define a copy constructor or override the = operator. Does Swift support something like that?

Answer 1

A copy constructor is nothing more than an initializer that takes another instance of the same type. Simply define such initializers for your class and struct with the appropriate deep copies.

class FooClass {
    var someValue: String = "123"

    init() {
    }

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

    // "Copy constructor"
    convenience init(_ other: FooClass) {
        self.init(someValue: other.someValue)
    }
}

struct TestStruct {
    var aValue: Int = 12
    var clsValue: FooClass

    init(aValue: Int, clsValue: FooClass) {
        self.aValue = aValue
        self.clsValue = FooClass(clsValue) // deep copy
    }

    // "Copy constructor"
    init(_ other: TestStruct) {
        self.init(aValue: other.aValue, clsValue: other.clsValue)
    }
}

var a = TestStruct(aValue: 10, clsValue: FooClass())
var b = TestStruct(a) // create new instance with its deep copy
b.clsValue.someValue = "abc"
print(a.clsValue.someValue) // prints 123