Swift 2.0 Study Notes (Day 30)-Choose a class or a struct?

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classes and structs are very similar, and in many cases there is no difference. If you are a designer when designing a system, do you design a class or struct as a type?  

Class and struct similarities and differences:

Classes and structs have the following functions:

• Defining Storage Properties
• Defining methods
• Define Subscript
• Defining constructors
• definition extension
• Implementation Protocol  

• Features that only classes have:

• Ability to inherit another class
• Ability to check types of run-time objects
• destructor frees resources
• reference count allows one instance to have multiple references  

The principle of choice:

Structs are value types, each instance does not have a unique identity, and the following two array instances are inherently indistinguishable, and they can be replaced by each other.

var studentList1: [string]  = ["Zhang San", "John Doe", "Harry"]var StudentList2: [string]  = ["Zhang San", "John Doe", "Harry"]

But when we refer to classes, it is a reference type and each instance has a unique identity. Let's look at the following employee class Code:

class Employee { 

    var no   = 0       

    var name = ""  

    var job = ""   

    var salary = 0.0 

}

 

var emp1  =  Employee()

emp1.no = 100

emp1.name = "Tom"

emp1.job = "SALES"

emp1.salary = 9000

 

var emp2  =  Employee()

emp2.no = 100

emp2.name = "Tom"

emp2.job = "SALES"

emp2.salary = 9000

EMP1 and the EMP2 Two employee instances even though the content is exactly the same, it doesn't mean that they are the same employee, just similar. Each employee instance has a unique identity behind it.

let's look at the department again. Department structural body.

struct Department {

    var no: Int = 0

    var name: String = ""

}

 

var dept1 = Department()

dept1.no = 20

dept1.name = "Research"

 

var dept2 = Department()

dept2.no = 20

dept2.name = "Research"

DepartmentWhy is it designed to be a struct rather than a class, it depends on what we understand about two different departments, if we have the same department number (No) and the department name (namewe think that they are two of the same department, then we can putDepartmentdefined as a struct, which is associated with an employeeEmployeedifferent.

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Swift 2.0 Study Notes (Day 30)-Choose a class or a struct?