An F# Records is similar to a tuple, however, it contains named fields. For example,
type website =
{ title : string;
url : string }
Defining F# Records
A record is defined as a type using the type keyword, and the fields of the record are defined as a semicolon-separated list.
The syntax for defining a record is −
type recordName =
{ [ fieldName : dataType ] + }
Creating a Record
You can create a record by specifying the record’s fields. For example, let us create a website record named homepage −
let homepage = { Title = "Adglob Point"; Url = "www.adglob.in" }
The following examples will explain the concepts −
Example 1
This program defines a record type named website. Then it creates some records of type website and prints the records.
(* defining a record type named website *)
type website =
{ Title : string;
Url : string }
(* creating some records *)
let homepage = { Title = "Adglob Point"; Url = "www.adglob.in" }
let cpage = { Title = "Learn C"; Url = "www.adglob.in/cprogramming/index.htm" }
let fsharppage = { Title = "Learn F#"; Url = "www.adglob.in/fsharp/index.htm" }
let csharppage = { Title = "Learn C#"; Url = "www.adglob.in/csharp/index.htm" }
(*printing records *)
(printfn "Home Page: Title: %A \n \t URL: %A") homepage.Title homepage.Url
(printfn "C Page: Title: %A \n \t URL: %A") cpage.Title cpage.Url
(printfn "F# Page: Title: %A \n \t URL: %A") fsharppage.Title fsharppage.Url
(printfn "C# Page: Title: %A \n \t URL: %A") csharppage.Title csharppage.Url
When you compile and execute the program, it yields the following output −
Home Page: Title: "adglob Point"
URL: "www.adglob.in"
C Page: Title: "Learn C"
URL: "www.adglob.in/cprogramming/index.htm"
F# Page: Title: "Learn F#"
URL: "www.adglob.in/fsharp/index.htm"
C# Page: Title: "Learn C#"
URL: "www.adglob.in/csharp/index.htm"
Example 2
type student =
{ Name : string;
ID : int;
RegistrationText : string;
IsRegistered : bool }
let getStudent name id =
{ Name = name; ID = id; RegistrationText = null; IsRegistered = false }
let registerStudent st =
{ st with
RegistrationText = "Registered";
IsRegistered = true }
let printStudent msg st =
printfn "%s: %A" msg st
let main() =
let preRegisteredStudent = getStudent "Zara" 10
let postRegisteredStudent = registerStudent preRegisteredStudent
printStudent "Before Registration: " preRegisteredStudent
printStudent "After Registration: " postRegisteredStudent
main()
When you compile and execute the program, it yields the following output −
Before Registration: : {Name = "Zara";
ID = 10;
RegistrationText = null;
IsRegistered = false;}
After Registration: : {Name = "Zara";
ID = 10;
RegistrationText = "Registered";
IsRegistered = true;}
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