structure vs class in swift language

Question

Here's an example with a class. Note how when the name is changed, the instance referenced by both variables is updated. Bob is now Sue, everywhere that Bob was ever referenced.

class SomeClass {
    var name: String
    init(name: String) {
        self.name = name
    }
}

var aClass = SomeClass(name: "Bob")
var bClass = aClass // aClass and bClass now reference the same instance!
bClass.name = "Sue"

println(aClass.name) // "Sue"
println(bClass.name) // "Sue"

And now with a struct we see that the values are copied and each variable keeps it's own set of values. When we set the name to Sue, the Bob struct in aStruct does not get changed.

struct SomeStruct {
    var name: String
    init(name: String) {
        self.name = name
    }
}

var aStruct = SomeStruct(name: "Bob")
var bStruct = aStruct // aStruct and bStruct are two structs with the same value!
bStruct.name = "Sue"

println(aStruct.name) // "Bob"
println(bStruct.name) // "Sue"

So for representing a stateful complex entity, a class is awesome. But for values that are simply a measurement or bits of related data, a struct makes more sense so that you can easily copy them around and calculate with them or modify the values without fear of side effects.

Both class and structure can do:

• Define properties to store values
• Define methods to provide functionality
• Be extended
• Conform to protocols
• Define intialisers
• Define Subscripts to provide access to their variables

Only class can do:

• Inheritance
• Type casting
• Define deinitialisers
• Allow reference counting for multiple references.

struct are value types. It means that if you copy the instance of the structure to another variable, it's just copied to the variable.

Example for Value Type

struct Resolution {
    var width = 2
    var height = 3
}

let hd = Resolution(width: 1920, height: 1080)
var cinema = hd //assigning struct instance  to variable
println("Width of cinema instance is \(cinema.width)")//result is 1920
println("Width of hd instance is \(hd.width)")//result is 1920

cinema.width = 2048

println("Width of cinema instance is \(cinema.width)")//result is 2048
println("Width of hd instance is \(hd.width)")//result is 1920

Classes are reference types. It means that if you assign an instance of the class to a variable, it will hold only the reference to the instance and not the copy.

This question seems to be duplicate but regardless, the following would answer most of the use case:

1. One of the most important differences between structures and classes is that structures are value types and are always copied when they are passed around in your code, and classes are reference type and are passed by reference.

2. Also, classes have Inheritance which allows one class to inherit the characteristics of another.

3. Struct properties are stored on Stack and Class instances are stored on Heap hence, sometimes the stack is drastically faster than a class.

4. Struct gets a default initializer automatically whereas in Class, we have to initialize.

5. Struct is thread safe or singleton at any point of time.

And also, To summarise the difference between structs and classes, it is necessary to understand the difference between value and reference types.

1. When you make a copy of a value type, it copies all the data from the thing you are copying into the new variable. They are 2 separate things and changing one does not affect the other.
2. When you make a copy of a reference type, the new variable refers to the same memory location as the thing you are copying. This means that changing one will change the other since they both refer to the same memory location. The sample code below could be taken as reference.

// sampleplayground.playground

  class MyClass {
        var myName: String
        init(myName: String){
            self.myName = myName;
        }
    }

    var myClassExistingName = MyClass(myName: "DILIP")
    var myClassNewName = myClassExistingName
    myClassNewName.myName = "John"


    print("Current Name: ",myClassExistingName.myName)
    print("Modified Name", myClassNewName.myName)

    print("*************************")

    struct myStruct {
        var programmeType: String
        init(programmeType: String){
            self.programmeType = programmeType
        }
    }

    var myStructExistingValue = myStruct(programmeType: "Animation")
    var myStructNewValue = myStructExistingValue
    myStructNewValue.programmeType = "Thriller"

    print("myStructExistingValue: ", myStructExistingValue.programmeType)
    print("myStructNewValue: ", myStructNewValue.programmeType)

Output:

Current Name:  John
Modified Name John
*************************
myStructExistingValue:  Animation
myStructNewValue:  Thriller