Swift Structs Tutorial with Examples

What is Struct?
Struct vs Class
Constructor of Struct
Methods and properties of Struct
Struct and Protocol

1. What is Struct?

In Swift, Struct (structure) is a special type of value, it creates a variable, to store multiple values, but the values are related to each other.

For example, information about an employee include:

Employee number
Employee name
Position

You can create 3 variables to store the information above of employee. However you can create a Struct to store all three information on in a single variable.

Swift uses struct keyword to declare a Struct.

Employee.swift

import Foundation 

struct Employee {
   var empNumber:String
   var empName:String
   var position:String
   // Constructor.
   init(empNumber:String, empName:String, position:String) {
      self.empNumber = empNumber;
      self.empName = empName;
      self.position = position;
  }
}

For example, use Struct:

EmployeeTest.swift

import Foundation  

func test_EmployeeStruct()     { 
    // Create a variable from Employee struct
    let john = Employee(empNumber:"E01",empName: "John",position: "CLERK")
    
    print("Emp Number: " + john.empNumber)
    print("Emp Name: " + john.empName)
    print("Emp Position: " + john.position) 
}

Edit main.swift:

main.swift

import Foundation

test_EmployeeStruct()

Running the example:

Emp Number: E01
Emp Name: John
Emp Position: CLECK

2. Struct vs Class

Struct is commonly used to create an object to store the value, while the class is using more diversely.

Struct does not allow inheritance from a class or another struct.
But Struct allows inheritance from one or more Protocol.

If struct appears as a parameter in a function (or method), it is passed as a value. Meanwhile, if the instance of a class appears as a parameter in a function (or method) it is passed as a reference.

StructVsClass.swift

import Foundation

// A class
class MyClass  { 
    var name: String = "Abc" 
} 
// A struct
struct MyStruct { 
    var name: String = "Abc" 
} 
// A function, 2 parameters
// First parameter is a class, and second parameter is a struct.
func passToMe( myClass: MyClass, myStruct: MyStruct)   { 
    // Change value to 'name' field.
    myClass.name = "New Name"
    
    // Can not change value to field of this struct.
    // (It is a copy,its fields become constants and can not be changed.
    // myStruct.name = "New Name" ***
}  
func test_passToMe()   { 
    // An object of MyClass.
    var  mc = MyClass()
    
    print("mc.name = \(mc.name)") // Abc
    
    // A value of MyStruct.
    var ms = MyStruct() 
    
    print("Call passToMe function")
    
    // Pass to passToMe() function.
    // Note: The first parameter does not require a Label.
    passToMe( mc, myStruct: ms) 
    
    print("mc.name = \(mc.name)") // New Name 
}

Running the example:

mc.name = Abc
Call passToMe function
mc.name = New Name

3. Constructor of Struct

Struct can have Constructors but do not have Destructor

Here are few notes for the Constructor:

You can write one or more constructor for struct.
In the constructor you must assign values to all fields that don't have value.

4. Methods and properties of Struct

Struct can have methods and properties.

Book.swift

import Foundation

struct Book  {
   // Property
   var title:String    {
      get    {
        return self.title;
      }
      set (value)   {
        self.title = value
      }
   }
   // Property
   var author:String    {
       get {
        return self.author;
       }
       set(value)  {
           self.author = value;
       }
   }
   // Constructor.
   init(  title:String, author:String)  {
      self.title = title;
      self.author = author;
   }
   // Method.
   func getInfo() -> String     {
       return "Book Title: " + self.title + ", Author: " + self.author;
   }
}

See more about properties at:
Swift Properties

5. Struct and Protocol

Struct can inherit from one or more Protocols.

TODO: