Swift Class versus Structure

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In Swift Just like classes play a important role , Structure do play a important role.

What could be the notable difference?
First one is Structure is pass by value and Classes are pass by reference.  Below is a simple example to understand the meaning of it.



func getAddress(_ object: Any)->String{
    var newObject = object
    var address:String = String("Could Not CalculateAddress")
    withUnsafePointer(to: &newObject) {
        
        address = "\($0)"
    }
    return address
}

func getAddressForClass(_ object:AnyObject) -> Any {
    return Unmanaged<AnyObject>.passUnretained(object).toOpaque()
}

//Structure
struct User{
    var name:String
    var userId:Int
}

func changeStructuredValue(_ inputStruct:User){
    var newInputStruct = inputStruct
    newInputStruct.name =  "Rose"
    print("Modifying Struct , Address Location= \(getAddress(newInputStruct))")
}

var structUser = User(name: "John", userId: 1)
print("Original Structure = \(structUser) Address Location= \(getAddress(structUser))")
changeStructuredValue(structUser)
print("Modified Structure = \(structUser) Address Location= \(getAddress(structUser))")

print("\n\n")


///Class
class Person {
    var personName : String?
    var personId   : Int?
}

func changeClassValue(_ inputPerson: Person){
    inputPerson.personName = "Eddie"
    print("Modifying Class Address Location= \(getAddressForClass(inputPerson))")
}

var person = Person()
person.personName = "ED"
person.personId = 189
print("Original Class = \(person.personName) Address Location= \(getAddressForClass(person))")
changeClassValue(person)

print("Modified Class = \(person.personName) Address Location= \(getAddressForClass(person))")




-------The output of the above code would be--------------

Original Structure = User(name: "John", userId: 1) Address Location= 0x00007fff5f2af048
Modifying Struct , Address Location= 0x00007fff5f2aef58
Modified Structure = User(name: "John", userId: 1) Address Location= 0x00007fff5f2af048



Original Class = Optional("ED") Address Location= 0x0000618000072500
Modifying Class Address Location= 0x0000618000072500

Modified Class = Optional("Eddie") Address Location= 0x0000618000072500

You might have noticed , changeStructuredValue does change the value and is local to the scope. It creates a new copy for the function changeStructuredValue.

 On the other side for the class the address remains the same before and after the modifying the value.

This was small example , that could help understanding this concept. Please write in your comments for any further feedback.


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