Swift World: Design Patterns — Simple Factory
If we want to learn a programming language, we need to live with it. It means to use Swift as much as possible. Today, we will start talking about design patterns in Swift. In addition to simple explanation, we also try to give figures, samples, use cases, etc. Let’s get started.
The first pattern is simple factory. Simply speaking, we build a factory to produce different objects which belong to the same type. As in the following figure and code, we have different types of cars, sedan, SUV, and maybe van. They all conform to protocol Car. It means the protocol defines common interface for cars. The specific car type implement their own logic.
If we want to add van, we create van class.
enum CarType {
case sedan, SUV, van
}class Van: Car {
func drive() {
print("drive a van")
}
}
Then the instance
let van = Van()
van.drive()Let’s try simple factory pattern to do the same thing. We need a factory to do the job to produce different types of cars.
class Factory {
static func produceCar(type: CarType) -> Car {
switch type {
case .sedan:
return Sedan()
case .SUV:
return SUV()
}
}
}let sedan = Factory.produceCar(type: .sedan)
sedan.drive()
let suv = Factory.produceCar(type: .SUV)
suv.drive()
Obviously, it is the factory which creates different instances of cars. Then what if we want to add van? The van class have been defined. So here we need to change the factory to enable it to produce van.
class Factory {
static func produceCar(type: CarType) -> Car {
switch type {
case .sedan:
return Sedan()
case .SUV:
return SUV()
case .van
return Van()
}
}
}let sedan = Factory.produceCar(type: .sedan)
sedan.drive()
let suv = Factory.produceCar(type: .SUV)
suv.drive()
let van = Factory.produceCar(type: .van)
van.drive()
That’s all simple factory pattern does. But why do we need this pattern? It separates the creation from usage and move the responsibility to a specific role. Or speak in professional terms, it helps loose coupling. Let’s assume the initialization logic of sedan is changed one day. We don’t need to change every creation in the whole project. To change the logic in factory is all we need to do.
In next blog of this series, we will talk about Factory Method Pattern.
A complete collection for all patterns is here.
