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Swift Structs Tutorial with Examples

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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.
  1. Struct does not allow inheritance from a class or another struct.
  2. 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:
  1. You can write one or more constructor for struct.
  2. 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:
  • TODO Link?

5- Struct and Protocol

Struct can inherit from one or more Protocols.
  • TODO:

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