Inheritance is used to model the "is-a" relationship, or subtyping, in object-oriented programming.
inherit keyword in a class declaration.inherit keyword by default, it inherits object class.The basic syntax for inheritance is shown below.
type MyDerived(...) =
inherit MyBase(...)
base is available in derived classes and refers to the base class instance. It is used like the self-identifier.The following example shows a simple inheritance.
type Person(name:string, age:int) =
class
member this.DisplayName() = printf"Name: %s\nAge: %d\n" name age
end
type Employee(name, age:int, salary:int) =
class
inherit Person(name, age)
member this.DisplaySalary() = printf"Salary = $%d" salary
end
let emp = new Employee("Andy", 23, 4500)
emp.DisplayName()
emp.DisplaySalary()
In F#, virtual members work differently as compared to other .NET languages. To declare a new virtual member, you can use the abstract keyword. You do this regardless of whether you provide a default implementation for that method.
The following syntax shows how to define a virtual method in a base class.
abstract member [method-name] : [type]
default [self-identifier].[method-name] [argument-list] = [method-body]
You can define a virtual method in a derived class as shown in the below syntax.
override [self-identifier].[method-name] [argument-list] = [method-body]
If you omit the default implementation in the base class, the base class becomes an abstract class.
The following example shows the declaration of a new virtual method TopSpeed in a base class and how to override it in a derived class.
type Vehicle() =
abstract member TopSpeed: unit -> int
default this.TopSpeed() = 100
type Car() =
inherit Vehicle()
override this.TopSpeed() = base.TopSpeed() + 100
// test
let vehicle = new Vehicle()
printfn "vehicle.TopSpeed = %i" <| vehicle.TopSpeed()
let car = new Car()
printfn "rocket.TopSpeed = %i" (car.TopSpeed())
To override an abstract method or property in a subclass, use the override keyword instead of the member keyword.