Swift customer design sample – The.Swift.Dev.

A fundamental 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? Truly this sample is what offers SwiftUI superpowers, let me present you the way it works.

open class View {}

last class FirstView: View {}
last class SecondView: View {}
last 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 lessons, this may 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 lengthen our lessons to simply accept this customer object and calculate the consequence 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 attainable 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 lessons.

A generic customer

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

open class View {}

last class FirstView: View {}
last class SecondView: View {}
last 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<O>(_ object: O) -> R
}

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

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

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

extension HeightVisitor: Customer {

    func go to<O>(_ 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 lengthen your objects to simply accept a generic customer kind. If you happen to select this strategy you continue to should implement the generic go to methodology on the Customer, solid the thing kind and name the kind particular go to methodology. This fashion we moved the go to name logic into the customer. 🙃

Because the views already conforms to the AcceptsVisitor protocol, we are able to simply lengthen them with different guests. For instance we are able to outline a colour customer like this:

struct ColorVisitor: Customer {
    func go to(_ view: FirstView) -> String { "crimson" }
    func go to(_ view: SecondView) -> String { "inexperienced" }
    func go to(_ view: ThirdView) -> String { "blue" }
    
    func go to<O>(_ 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 possibly can see it is fairly good that we are able to obtain this type of dynamic object extension logic by means of guests. If you wish to see a sensible UIKit instance, be happy to check out this text. Underneath 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 suggest to study extra about it. 💪