F# - 記錄

一個記錄類似於元組，但是它包含命名欄位。例如，

type website =
   { title : string;
     url : string }

定義記錄

記錄是用type關鍵字定義的一種型別，記錄的欄位定義為用分號分隔的列表。

定義記錄的語法為：

type recordName =
   { [ fieldName : dataType ] + }

建立記錄

您可以透過指定記錄的欄位來建立記錄。例如，讓我們建立一個名為homepage的website記錄：

let homepage = { Title = "TutorialsPoint"; Url = "www.tutorialspoint.com" }

以下示例將解釋這些概念：

示例 1

此程式定義了一個名為website的記錄型別。然後它建立一些website型別的記錄並列印這些記錄。

(* defining a record type named website *)
type website =
   { Title : string;
      Url : string }

(* creating some records *)
let homepage = { Title = "TutorialsPoint"; Url = "www.tutorialspoint.com" }
let cpage = { Title = "Learn C"; Url = "www.tutorialspoint.com/cprogramming/index.htm" }
let fsharppage = { Title = "Learn F#"; Url = "www.tutorialspoint.com/fsharp/index.htm" }
let csharppage = { Title = "Learn C#"; Url = "www.tutorialspoint.com/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

編譯並執行程式後，將產生以下輸出：

Home Page: Title: "TutorialsPoint"
       URL: "www.tutorialspoint.com"
C Page: Title: "Learn C"
      URL: "www.tutorialspoint.com/cprogramming/index.htm"
F# Page: Title: "Learn F#"
      URL: "www.tutorialspoint.com/fsharp/index.htm"
C# Page: Title: "Learn C#"
      URL: "www.tutorialspoint.com/csharp/index.htm"

示例 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()

編譯並執行程式後，將產生以下輸出：

Before Registration: : {Name = "Zara";
   ID = 10;
   RegistrationText = null;
   IsRegistered = false;}
After Registration: : {Name = "Zara";
   ID = 10;
   RegistrationText = "Registered";
   IsRegistered = true;}