iOS Swift 5 Structs Vs Classes:
Hello there!.. Let us deep dive into the Structs vs Classes and see how similar they and also how different they are.
How difference Structs and classes are:
Initializations
Classes required manual initializer using init method in it.
Example :
Class PersonClass
{
var firstName : String?
var lastName : String?
var age : Int?
init(firstName : String , lastName : String, age : Int)
{
self.firstName = firstName
self.lastName = lastName
self.age = age
}
}
Structs have memberwise initializers where we don’t manually have to initialize using init method and also objects in the Struct don’t have to be optionals.
Example:
Struct PersonStruct
{
var firstName : String?
var lastName : String?
var age : Int?
}
Why we don’t need optionals for objects in structs? This will be answered when we explain about Stack and Heap later in this document.
Value Type VS Reference Type
Structs are value type where classes are reference type
To understand the concept let's relate this with a day to day example, Imagine Struct is an excel sheet which we share with someone so that they have a copy where they can edit But class is like google docs when you share it with someone the same document will get shared and both of them will edit the same doc.
What is meant by Reference Type?
When you copy a class variable to a new variable, We are copying the reference of the class variable to the new variable. If we change the value of one variable, that will affect the other as well.
Lets see the example:
var person1 = PersonStruct( firstName : “Daisy” , lastName : “Rose”, age : 5)
var person2 = person1 (Here are we copying the reference of person1 to person 2)
person2.firstName = “Jasmine”
print(person1.firstname) (This will print “Jasmine” Because person2
is a reference of person1)
What is meant by Value type?
When you copy a Struct variable to a new variable, we are not copying the reference of it. But We are copying the object value and creating the whole new object.
Let me explain with an example.
var person1 = PersonStruct( firstName : “Daisy” , lastName : “Rose”, age : 5)
var person2 = person1 (Here are we copying the value of person1 to person 2 and
creating a new object lets see what that mean)
person2.firstName = “Jasmine”
print(person1.firstname) (this will print “Daisy” but not “Jasmine” Because person2
is not a reference of person1 but the copy of person1 and
Person2 is a whole new object)
In short, person1 and person2 are independent on each other
Even though it's very confusing, we will try to clear the air by the end of this document.
Functions
Functions of a class are mutable where functions in the Struct are immutable.
When you create a function which modifies struct , the function should be muted using “mutating” keyword
Eg :
Struct PersonStruct
{
var firstName : String?
var lastName : String?
var age : Int?
mutating func uppercaseFirstName
{
}
}
Inheritance & Subclassing
Here you find the answers for a very important question, i.e, When to use Structs and When to use classes?
Inheritance and Subclassing is supported in classes where they are not in Structs, When there is not dependency we will surely go for Structs.
This makes Structs light weight
Stack VS Heap
When you create a variable of Structs, it will get created in stack and removed when it returns. Stack is very efficient and very fast. This is the reason why we don't have to make variables optionals. When the object is not having a value stack will delete the object.
When you create a variable of classes, it will get created in Heap and It is not easy to clear the memory , But Heap is a huge amount of memory where system can request and dynamically allocate memory.
Similarities of Structs and Classes are:
Both have function
Both have confirmed to protocols
Both have computed properties
Quick Distinguishing:
