面向对象编程中最重要的概念之一是继承.继承允许我们根据另一个类定义一个类，这使得创建和维护应用程序变得更容易.这也提供了重用代码功能和快速实现时间的机会.
创建类时，程序员可以指定新类，而不是编写全新的数据成员和成员函数.应该继承现有类的成员.这个现有的类称为基类，新类称为派生类.
继承的思想实现了IS-A关系.例如，哺乳动物IS动物，狗IS-A哺乳动物因此狗IS-A动物等等.
子类派生自已定义的基类.子类继承基类的成员，并且有自己的成员.
使用 inherit 关键字定义子类，如下所示 :
type MyDerived(...) = inherit MyBase(...)
在F＃中，一个类最多只能有一个直接基类.如果未使用 inherit 关键字指定基类，则该类隐式继承自Object.
请注意&减去;
派生类的用户可以使用基类的方法和成员，例如派生类的直接成员.
让绑定和构造函数参数对类是私有的，因此无法从派生类访问.
关键字 base 是指基类实例.它像自我标识符一样使用.
type Person(name) =
member x.Name = name
member x.Greet() = printfn "Hi, I'm %s" x.Name
type Student(name, studentID : int) =
inherit Person(name)
let mutable _GPA = 0.0
member x.StudentID = studentID
member x.GPA
with get() = _GPA
and set value = _GPA <- value
type Teacher(name, expertise : string) =
inherit Person(name)
let mutable _salary = 0.0
member x.Salary
with get() = _salary
and set value = _salary <- value
member x.Expertise = expertise
//using the subclasses
let p = new Person("Mohan")
let st = new Student("Zara", 1234)
let tr = new Teacher("Mariam", "Java")
p.Greet()
st.Greet()
tr.Greet()当你编译并执行程序时，它产生以下输出 :
Hi, I'm Mohan Hi, I'm Zara Hi, I'm Mariam
您可以覆盖基类方法的默认行为，并在子类或派生类中以不同方式实现它.
默认情况下，F＃中的方法不可覆盖.
要覆盖派生类中的方法，必须使用抽象和默认关键字将方法声明为可覆盖，如下所示 :
type Person(name) = member x.Name = name abstract Greet : unit -> unit default x.Greet() = printfn "Hi, I'm %s" x.Name
现在，问候 Person类的方法可以在派生类中重写.以下示例演示了此 :
type Person(name) =
member x.Name = name
abstract Greet : unit -> unit
default x.Greet() = printfn "Hi, I'm %s" x.Name
type Student(name, studentID : int) =
inherit Person(name)
let mutable _GPA = 0.0
member x.StudentID = studentID
member x.GPA
with get() = _GPA
and set value = _GPA <- value
override x.Greet() = printfn "Student %s" x.Name
type Teacher(name, expertise : string) =
inherit Person(name)
let mutable _salary = 0.0
member x.Salary
with get() = _salary
and set value = _salary <- value
member x.Expertise = expertise
override x.Greet() = printfn "Teacher %s." x.Name
//using the subclasses
let p = new Person("Mohan")
let st = new Student("Zara", 1234)
let tr = new Teacher("Mariam", "Java")
//default Greet
p.Greet()
//Overriden Greet
st.Greet()
tr.Greet()当你编译并执行程序时，它产生以下输出 :
Hi, I'm Mohan Student Zara Teacher Mariam.
有时你需要提供一个不完整的对象实现，不应该在现实.稍后，其他程序员应该为完整的实现创建抽象类的子类.
例如，学校管理系统中不需要Person类.但是，将需要学生或教师课程.在这种情况下，您可以将Person类声明为抽象类.
AbstractClass 属性告诉编译器该类有一些抽象成员.
您无法创建抽象类的实例，因为该类未完全实现.
以下示例演示了此 :
[<AbstractClass>]
type Person(name) =
member x.Name = name
abstract Greet : unit -> unit
type Student(name, studentID : int) =
inherit Person(name)
let mutable _GPA = 0.0
member x.StudentID = studentID
member x.GPA
with get() = _GPA
and set value = _GPA <- value
override x.Greet() = printfn "Student %s" x.Name
type Teacher(name, expertise : string) =
inherit Person(name)
let mutable _salary = 0.0
member x.Salary
with get() = _salary
and set value = _salary <- value
member x.Expertise = expertise
override x.Greet() = printfn "Teacher %s." x.Name
let st = new Student("Zara", 1234)
let tr = new Teacher("Mariam", "Java")
//Overriden Greet
st.Greet()
tr.Greet()当你编译并执行程序时，它会产生以下输出 :
Student Zara Teacher Mariam.
