struct vs class in swift

STRUCT vs CLASS

Laurentiu Ungur, iOS Developer @P3-Digital Services

Why I should use a struct instead of a class ?

1. POWERFUL

PROBLEM WITH SUBCLASSING ?

struct Vehicle {let model: Stringlet price: Double

}

enum VehicleType {case car(licensePlate: String)case bicycle(chainRings: Int)

}

struct Vehicle {let model: Stringlet price: Double

let type: VehicleType }

let car = Vehicle(model: “X”, price: 200, type: .car(licensePlate: “CJ”))

let bicycle = Vehicle(model: “A”, price: 10, type: .bicycle(chainRings: 100))

2. VALUE SEMANTICS

3. AUTOMATIC INITIALIZER

struct Car {let brand: Stringlet model: Stringlet price: Double

}


init(brand: String, model: String, price: Double) {self.brand = brandself.model = modelself.price = price

}}

let myCar = Car(brand: “Tesla”, model: “S”, price: 100)


}

let myCar = Car(brand: “Tesla”, model: “S”, price: 100)

4. SPEED

40xFaster

Swift 1

github.com/knguyen2708/StructVsClassPerformance

37 000 000xFaster

Swift 2 - Whole Module Optimization


14 000 000xFaster

Swift 3 - Whole Module Optimization


Use final keyword

unsplash.com/collections/328902/cow

COW (Copy-On-Write)

let a = [1, 2, 3]

var b = a // not copied

b.append(4) // now it’s copied

When I should use a struct ?● The data will be used in code across multiple

threads


threads● Copies should have independent state


threads● Copies should have independent state● Encapsulates a few relatively simply data

values

When I should use a class ?● You want to create shared, mutable state

When I should use a class ?● You want to create shared, mutable state● You want to create complex frameworks like

Cocoa or Cocoa Touch

Still undecided ?

Design with struct as default,

fallback to class if it’s really needed.

THANKS !

struct vs class in swift

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