Classes are types that represent objects that can have properties, methods, and events. Classes represent the fundamental description of .NET object types; the class is the primary type concept that supports object-oriented programming in F#.
The basic syntax of the class declaration is as follows.
type [access-modifier] type-name [type-params] [access-modifier] ( parameter-list ) [ as identifier ] =
[ class ]
[ inherit base-type-name(base-constructor-args) ]
[ let-bindings ]
[ do-bindings ]
member-list
...
[ end ]
// Mutually recursive class definitions:
type [access-modifier] type-name1 ...
and [access-modifier] type-name2 ...
...
type-name: It is any valid identifier.type-params: Describes optional generic type parameters. It consists of type parameter names and constraints enclosed in angle brackets (< and >).parameter-list: Describes constructor parameters. The first access modifier pertains to the type; the second pertains to the primary constructor. In both cases, the default is public.inherit: You specify the base class for a class by using the inherit keyword. You must supply arguments, in parentheses, for the base class constructor.let: You declare fields or function values that are local to the class by using let bindings.do: The do-bindings section includes code to be executed upon object construction.member-list: Consists of additional constructors, instance and static method declarations, interface declarations, abstract bindings, and property and event declarations.identifier: It is used with the optional as keyword gives a name to the instance variable, or self identifier, which can be used in the type definition to refer to the instance of the type.class and end: The class and end mark the start and end of the definition are optional.The following code shows a very simple class declaration.
type Author (firstName, lastName, age) =
member this.FirstName = firstName
member this.LastName = lastName
member this.Age = age
The object is an instance of a class to access the defined properties and methods. It is a concrete entity based on a class and is created at runtime. You can create an object using the new keyword followed by the name of the class.
type Author (firstName, lastName, age) =
member this.FirstName = firstName
member this.LastName = lastName
member this.Age = age
let author1 = new Author("Mark", "Upston", 25)
In F#, the constructor is considered to be just another function, so you can also call the constructor function without using the new keyword.
let author2 = Author("Adrian", "Christian", 31)
You can also initialize and display data through the method as shown below.
type Author() =
class
let mutable firstName = ""
let mutable lastName = ""
let mutable age = 0
member x.Insert(fName, lName, aAge) =
firstName <- fName
lastName <- lName
age <- aAge
member x.Display = Console.WriteLine(firstName + " " + lastName + " (" + age.ToString() + ")")
end
let author1 = new Author()
author1.Insert("Mark", "Upston", 25)
author1.Display