Swift type attribute and its attentions

One 、 Type property details

Different from storage instance properties , You have to set the initial value for the storage type property

    Because types don't have instances like that init Initializer to initialize storage properties

The storage type attribute defaults to lazy, It will be initialized when it is used for the first time

    Even if it is accessed by multiple threads at the same time , Ensure that it is initialized only once

    The storage type property can be let

Enumeration types can also define type properties （ Storage type properties 、 Calculation type properties ）

Two 、 The singleton pattern

Because the type attribute has only one memory , So it can be used in the implementation of singleton .

struct Shape {
    static let width: Int = 0
}

enum ShapeEnum {
    static var width: Int = 0
    case s1, s2, s3, s4
}

class FileManager {
    public static let shared = FileManager()
    
    private init() {
    }
    
    func open() {
    }
    
    func close() {
    }
}

struct Point {
    var x: Int
    var y: Int
}