swift: passing by reference - swift

Question

Coming from JS, and trying to pass [JSON] by reference in swift, which is not possible, so I'm trying to wrap it in the object, and made a simple example using a primitive, which still not working, how can i wrap member a, so that changes in referenced object a affect b ? Thanks
class ExampleA {
var a = 0
init(a: Int) {
self.a = a
}
}
class ExampleB {
var a = 0
init(a: Int) {
self.a = a
}
func process(inout p: ExampleA) {
self.a = p.a
print(p.a)
}
}
var a = ExampleA(a: 15)
var b = ExampleB(a: 10)
b.process(&a)
print(b.a) // "15\n"
a.a = 25 // this does nothing to b????
print(b.a) // "15\n"

Answer 1

Your example fails because a is an Int, which is a value type.
When you do the assignment self.a = p.a, you're making a copy of the Int.
To achieve the reference semantics you want, you have to hold reference the ExampleA that's storing the value type. I think you got confused because of your variable naming, confusing the a : Int member of ExampleA with instances of ExampleA named a.
Here's a fix I put together. It gives ExampleB a computed property that transparently accesses the data in ExampleA.
class ExampleA {
var data = 0
init(data: Int) {
self.data = data
}
}
class ExampleB {
var a : ExampleA
var data : Int {
get {
return a.data
}
set {
a.data = newValue
}
}
init(data: Int) {
self.a = ExampleA(data: data)
}
func process(a: ExampleA) {
self.a = a
print(a.data)
}
}
var a = ExampleA(data: 15)
var b = ExampleB(data: 10)
b.process(a: a)
print(b.data) // "15\n"
a.data = 25
print(b.data) // "25\n"

Answer 2

Simple delegation works without any real need for inout or reference semantics:
class ExampleA {
var a = 0
init(a: Int) {
self.a = a
}
}
class ExampleB {
var aObject: ExampleA
init(a: ExampleA) {
self.aObject = a
}
func a() -> Int {
return aObject.a
}
}
var a = ExampleA(a: 15)
var b = ExampleB(a: a)
print(b.a())
a.a = 25
print(b.a())