Swift design mode: Prototype and swift design mode prototype

Swift design mode: Prototype and swift design mode prototype

Application scenarios:
You need to copy the object to create a new object.
Difficulties: Deep copy and light copy

Initializing a class or structure consumes a lot of memory resources and computing resources. However, copying can save these resources.
Copy of the value type is a deep copy.
So how to implement deep copy for the reference type?
The answer is the NSCopying protocol.

class ProductA: NSCopying {    var name: String    var price: Int    init(name:String,price:Int) {        self.name = name        self.price = price    }    func copy(with zone: NSZone? = nil) -> Any {        return ProductA.init(name: self.name, price: self.price)    }}

        let p = ProductA.init(name: "book", price: 10)        let c = p.copy() as! ProductA        c.name = "computer"        print(c.name,p.name)

In swift4, You can temporarily ignore the zone

What if the reference type contains a copy of the reference type?

copy(with zone: NSZone? = nil)

It is just a reference to the Copied object, rather than the object itself. It will also be a small copy:

class ProductA: NSCopying {    var name: String    var price: Int    var place: PlaceOfOrigin    init(name:String,price:Int, place:PlaceOfOrigin) {        self.name = name        self.price = price        self.place = place    }    func copy(with zone: NSZone? = nil) -> Any {        return ProductA.init(name: self.name, price: self.price,place:self.place)    }}class PlaceOfOrigin{    var country: String    var city: String    init(country:String, city:String) {        self.country = country        self.city = city    }}

let p = ProductA.init(name: "book", price: 10, place: PlaceOfOrigin.init(country: "American", city: "NewYork"))        let c = p.copy() as! ProductA        c.name = "computer"        c.place.city = "BeiJing"        print(c.name,c.place.city,p.name,p.place.city)

// Log: computer BeiJing book BeiJing

So how can we change it?

class ProductA: NSCopying {    var name: String    var price: Int    var place: PlaceOfOrigin    init(name:String,price:Int, place:PlaceOfOrigin) {        self.name = name        self.price = price        self.place = place    }    func copy(with zone: NSZone? = nil) -> Any {        return ProductA.init(name: self.name, price: self.price,place:self.place.copy() as! PlaceOfOrigin)    }}class PlaceOfOrigin:NSCopying{    var country: String    var city: String    init(country:String, city:String) {        self.country = country        self.city = city    }    func copy(with zone: NSZone? = nil) -> Any {        return PlaceOfOrigin.init(country: self.country, city: self.city)    }}

/// Log: computer BeiJing book NewYork

Next, let's look at array replication.

    var productAs = [ProductA.init(name: "computer", price: 10000, place: PlaceOfOrigin.init(country: "China", city: "BeiJing"))]

    func testArray(){        let otherProducts = self.productAs        otherProducts[0].name = "hh"        print(productAs[0].name,otherProducts[0].name)    }

/// Log: hh

OK. We can see that it is a small copy. How can we perform a deep copy?

let otherProducts =  productAs.map { (p) -> ProductA in            return p.copy() as! ProductA        }        otherProducts[0].name = "hh"        print(otherProducts[0].name)        print(productAs[0].name)

// Log: hh computer

There are several traps in the prototype mode.
1. Deep replication and latent Replication
2. Remember to use the cloned copy as the next prototype.