vickcoo

iOS Developer

Swift Structs and Classes: A Friendly Guide to Their Differences and Similarities

發佈於 Sep 20, 2023

When your're delving into the world of Swift programming, you'll inevitably come across two essential concepts: struct and class. In this guide, we'll unravel the mysteries of struct and class, making them easier to understand.

Similarities

  • Define properties (that including computed properties & property observer)
  • Define method
  • Define subscripts to provide access to their value
  • Define initializers
  • Be extended to expand their functionality beyond a default implementation
  • These have the ability to conform to protocols and then provide functionality

Differences

class have adiitional capabilities that structure don't have.

other difference thing.

  • Value Type & Reference Type
  • Mutable & Immutable
  • Memberwise Initializer

Syntax

this is the least code to define this struct and class, I'll show you actually example later.

struct SomeStruct {
}
class SomeClass {
}

Value Type & Reference Type

Swift struct is Value Type, this means any properties in struct instance, they always copy when they're passed around in your code.

struct Person {
    var name: String
    var age: Int
}

let andrew = Person(name: "Andrew", age: 22)
var eric = andrew

eric.age = 41

print(andrew.age) // print: 22
print(eric.age) // print: 41

And class is Reference Type, that aren't copied when they're passed. That reference same instance. For example, similar we defined struct above

class Person {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}

let andrew = Person(name: "Andrew", age: 22)
var eric = andrew

eric.age = 41

print(andrew.age) // print: 41
print(eric.age) // print: 41

Initializers

In Swift, when you create a struct and define properties, struct automatically get a initializer called Memberwise Initializer. but your must manually define a iniitializer in class

// struct
struct Person {
    var name: String
    var age: Int
}
let leo = Person(name: "Leo", age: 32)

// class
class Person {
    var name: String
    var age: Int

    init(name: String, age: Int) {
        self.name = name
        self.age = age
    }
}
let leo = Person(name: "Leo", age: 32)

Mutating

you can't modify any properties insdie method in struct by default, the solution is mark it using mutating keyword, like this:

struct Person {
    var name: String

    mutating func setName(name: String) {
        self.name = name
    }
}

Reference