Swift customer design sample – The.Swift.Dev.

A primary customer instance

The customer design sample is among the behavioral patterns, it’s used to increase an object with a given performance with out really modifying it. Sounds cool, proper? Really this sample is what offers SwiftUI superpowers, let me present you the way it works.

open class View {}

closing class FirstView: View {}
closing class SecondView: View {}
closing class ThirdView: View {}

struct HeightVisitor {
    func go to(_ view: FirstView) -> Float { 16 }
    func go to(_ view: SecondView) -> Float { 32 }
    func go to(_ view: ThirdView) -> Float { 64 }
}

protocol AcceptsHeightVisitor {
    func settle for(_ customer: HeightVisitor) -> Float
}

extension FirstView: AcceptsHeightVisitor {
    func settle for(_ customer: HeightVisitor) -> Float { customer.go to(self) }
}

extension SecondView: AcceptsHeightVisitor {
    func settle for(_ customer: HeightVisitor) -> Float { customer.go to(self) }
}

extension ThirdView: AcceptsHeightVisitor {
    func settle for(_ customer: HeightVisitor) -> Float { customer.go to(self) }
}

let customer = HeightVisitor()
let view1: AcceptsHeightVisitor = FirstView()
let view2: AcceptsHeightVisitor = SecondView()
let view3: AcceptsHeightVisitor = ThirdView()


print(view1.settle for(customer))
print(view2.settle for(customer))
print(view3.settle for(customer))

First we outline our customized view courses, it will assist to visualise how the sample works. Subsequent we outline the precise HeightVisitor object, which can be utilized to calculate the peak for every view kind (FirstView, SecondView, ThirdView). This fashion we do not have to change these views, however we are able to outline a protocol AcceptsHeightVisitor, and prolong our courses to simply accept this customer object and calculate the outcome utilizing a self pointer. 👈

On the decision aspect we are able to provoke a brand new customer occasion and easily outline the views utilizing the protocol kind, this fashion it’s potential to name the settle for customer methodology on the views and we are able to calculate the peak for every kind with out altering the inner construction of those courses.

A generic customer

We will additionally make this sample extra generic by making a Swift protocol with an related kind.

open class View {}

closing class FirstView: View {}
closing class SecondView: View {}
closing class ThirdView: View {}

struct HeightVisitor {
    func go to(_ view: FirstView) -> Float { 16 }
    func go to(_ view: SecondView) -> Float { 32 }
    func go to(_ view: ThirdView) -> Float { 64 }
}

protocol Customer {
    associatedtype R
    func go to(_ object: O) -> R
}

protocol AcceptsVisitor {
    func settle forCustomer>(_ customer: V) -> V.R
}

extension AcceptsVisitor {
    func settle forCustomer>(_ customer: V) -> V.R { customer.go to(self) }
}

extension FirstView: AcceptsVisitor {}
extension SecondView: AcceptsVisitor {}
extension ThirdView: AcceptsVisitor {}

extension HeightVisitor: Customer {

    func go to(_ object: O) -> Float {
        if let o = object as? FirstView {
            return go to(o)
        }
        if let o = object as? SecondView {
            return go to(o)
        }
        if let o = object as? ThirdView {
            return go to(o)
        }
        fatalError("Go to methodology unimplemented for kind (O.self)")
    }
}

let customer = HeightVisitor()
let view1: AcceptsVisitor = FirstView()
let view2: AcceptsVisitor = SecondView()
let view3: AcceptsVisitor = ThirdView()

print(view1.settle for(customer))
print(view2.settle for(customer))
print(view3.settle for(customer))

You should utilize the generic Customer protocol to outline the customer and the AcceptsVisitor protocol to simply prolong your objects to simply accept a generic customer kind. For those who select this strategy you continue to need to implement the generic go to methodology on the Customer, forged the item kind and name the sort particular go to methodology. This fashion we moved the go to name logic into the customer. 🙃

For the reason that views already conforms to the AcceptsVisitor protocol, we are able to simply prolong them with different guests. For instance we are able to outline a coloration customer like this:

struct ColorVisitor: Customer {
    func go to(_ view: FirstView) -> String { "purple" }
    func go to(_ view: SecondView) -> String { "inexperienced" }
    func go to(_ view: ThirdView) -> String { "blue" }
    
    func go to(_ object: O) -> String {
        if let o = object as? FirstView {
            return go to(o)
        }
        if let o = object as? SecondView {
            return go to(o)
        }
        if let o = object as? ThirdView {
            return go to(o)
        }
        fatalError("Go to methodology unimplemented for kind (O.self)")
    }
}

let customer = ColorVisitor()
let view1: AcceptsVisitor = FirstView()
let view2: AcceptsVisitor = SecondView()
let view3: AcceptsVisitor = ThirdView()

print(view1.settle for(customer))
print(view2.settle for(customer))
print(view3.settle for(customer))

As you may see it is fairly good that we are able to obtain this sort of dynamic object extension logic by way of guests. If you wish to see a sensible UIKit instance, be at liberty to check out this text. Below the hood SwiftUI closely makes use of the customer sample to attain some magical TupleView & ViewBuilder associated stuff. This sample is so cool, I extremely advocate to study extra about it. 💪