SWIFT

abstract class in swift

class Animal {
    func sound() {}
}

class Cat: Animal {
    override func sound() {
        print("miauw")
    }
}

class Dog: Animal {
    override func sound() {
        print("woof")
    }
}

Abstract classes in Swift

protocol Employee {
    var annualSalary: Int {get}
}

extension Employee {
    var biweeklySalary: Int {
        return self.annualSalary / 26
    }

    func logSalary() {
        print("$(self.annualSalary) per year or $(self.biweeklySalary) biweekly")
    }
}

struct SoftwareEngineer: Employee {
    var annualSalary: Int

    func logSalary() {
        print("overridden")
    }
}

let sarah = SoftwareEngineer(annualSalary: 100000)
sarah.logSalary() // prints: overridden
(sarah as Employee).logSalary() // prints: $100000 per year or $3846 biweekly