Are swift classes inside struct passed by copy during assignment?

Question

If I have a struct in swift with inside a class attribute and I copy the struct object, is the class attribute copied or passed by reference?

Answer 1

Passed by reference. You can test it. Declare:

class A{}
struct B { let a = A()}

then:

let b = B()
print("A = \(unsafeAddressOf(b.a))")//0x0000600000019450
let b_copy = b
print("A = \(unsafeAddressOf(b_copy.a))")//0x0000600000019450

Answer 2

All properties of a struct are copied (as if you assigned (=) each property of the old struct to the corresponding property of the new struct) when the struct is copied, regardless of type.

When you say "class attribute", I am assuming you mean a variable of reference type. (The type with the same name as a class denotes a reference type for references that point to objects of that class.) Copying a value of reference type (a reference) produces another reference that points to the same object. Note that "objects" are not values in Swift -- there are no "object types" -- rather, objects are always manipulated through references that point to them.