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 truly modifying it. Sounds cool, proper? Truly this sample is what offers SwiftUI superpowers, let me present you the way it works.

open class View {}

remaining class FirstView: View {}
remaining class SecondView: View {}
remaining 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 will outline a protocol AcceptsHeightVisitor, and prolong our lessons to simply accept this customer object and calculate the end result utilizing a self pointer. 👈

On the decision aspect we will 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 technique on the views and we will 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 {}

remaining class FirstView: View {}
remaining class SecondView: View {}
remaining 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 technique 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 need to use the generic Customer protocol to outline the customer and the AcceptsVisitor protocol to simply prolong your objects to simply accept a generic customer kind. Should you select this strategy you continue to should implement the generic go to technique on the Customer, solid the thing kind and name the sort particular go to technique. This fashion we moved the go to name logic into the customer. 🙃

For the reason that views already conforms to the AcceptsVisitor protocol, we will simply prolong them with different guests. For instance we will 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 technique 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 will obtain this type of dynamic object extension logic via guests. If you wish to see a sensible UIKit instance, be at liberty to try 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 be taught extra about it. 💪