Swift class

Swift classes are a general and flexible construct used to build code.

We can define properties (constants, variables) and methods for classes.

Unlike other programming languages, Swift does not require you to create separate interface and implementation files for custom classes. What you need to do is define a class in a single file, and the system will automatically generate an external interface for other code.

Comparison between classes and structures

Swift andStructuresThere are many similarities. The similarities are in:

• Define properties to store values

• Define methods to provide functionality

• Define computed properties to access values

• Define constructors to generate initial values

• Extend to add default implementation functionality

• Conform to protocols to provide standard functionality for a class

Compared to structures, classes have the following additional features:

• Inheritance allows a class to inherit the characteristics of another class

• Type casting allows the type of a class instance to be checked and interpreted at runtime

• A deinitializer allows an instance of a class to release any resources it has allocated

• Reference counting allows multiple references to a class

Syntax:

class classname {
　　　Definition　1
　　　Definition　2
　　　……
　　　Definition N
}

Class definition

class student{
　　　var studname: String
　　　var mark: Int　
　　　var mark2: Int　
}

Example class:

let studrecord = student()

Online Example

import　Cocoa
class MarksStruct {
　　　　var mark: Int
　　　　init(mark: Int) {
　　　　　　　　self.mark = mark
　　　　}
}
class studentMarks {
　　　　var mark =　300
}
let marks = studentMarks()
print("The score is (marks.mark)")

The output of the above program is as follows：

The score is　300

as a reference type

Class properties can be accessed through . to access. The format is:Example class name.property name:

import　Cocoa
class MarksStruct {
　　　var mark: Int
　　　init(mark: Int) {
　　　　　　self.mark = mark
　　　}
}
class studentMarks {
　　　var mark1　=　300
　　　var mark2　=　400
　　　var mark3　=　900
}
let marks = studentMarks()
print("Mark1　is (marks.mark1)")
print("Mark2　is (marks.mark2)")
print("Mark3　is (marks.mark3)")

The output of the above program is as follows：

Mark1　is　300
Mark2　is　400
Mark3　is　900

Identity operator

Because classes are reference types, there may be multiple constants and variables in the background that simultaneously refer to a particular instance of a class.

To determine whether two constants or variables refer to the same instance of a class, Swift has built-in two identity operators:

Online Example

import　Cocoa
class　SampleClass:　Equatable　{
　　　　let　myProperty:　String
　　　　init(s:　String)　{
　　　　　　　　myProperty　=　s
　　　　}
}
func　==(lhs:　SampleClass,　rhs:　SampleClass)　->　Bool　{
　　　　return　lhs.myProperty　==　rhs.myProperty
}
let　spClass1　=　SampleClass(s:　"Hello")
let　spClass2　=　SampleClass(s:　"Hello")
if　spClass1　===　spClass2　{//　false
　　　　print("Example of classes with the same reference　\(spClass1)")
}
if　spClass1　!==　spClass2　{//　true
　　　　print("Example of classes with different references　\(spClass2)")
}

The output of the above program is as follows：

Example of classes with different references　SampleClass