F# - 记录

记录与元组类似，但它包含命名字段。 例如，

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

定义记录

使用type关键字将记录定义为类型，记录的字段定义为分号分隔的列表。

定义记录的语法是 −

type recordName =
   { [ fieldName : dataType ] + }

创建记录

您可以通过指定记录的字段来创建记录。 例如，让我们创建一个名为 homepage 的 website 记录 −

let homepage = { Title = "TutorialsPoint"; Url = "www.w3ccoo.com" }

下面的例子将解释这些概念 −

示例 1

这个程序定义了一个名为website的记录类型。 然后它创建一些网站类型的记录并打印这些记录。

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

(* creating some records *)
let homepage = { Title = "TutorialsPoint"; Url = "www.w3ccoo.com" }
let cpage = { Title = "Learn C"; Url = "www.w3ccoo.com/cprogramming/index.html" }
let fsharppage = { Title = "Learn F#"; Url = "www.w3ccoo.com/fsharp/index.html" }
let csharppage = { Title = "Learn C#"; Url = "www.w3ccoo.com/csharp/index.html" }

(*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

当您编译并执行该程序时，它会产生以下输出 −

Home Page: Title: "TutorialsPoint"
       URL: "www.w3ccoo.com"
C Page: Title: "Learn C"
      URL: "www.w3ccoo.com/cprogramming/index.html"
F# Page: Title: "Learn F#"
      URL: "www.w3ccoo.com/fsharp/index.html"
C# Page: Title: "Learn C#"
      URL: "www.w3ccoo.com/csharp/index.html"

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()

当您编译并执行该程序时，它会产生以下输出 −

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