F# 探险之旅－面向对象编程（上）

#light
let myStr = "A string value."
let myObj = (myStr :> obj)

#light
open System.Windows.Forms
let myCtrls = 
    [| (new Button() :> Control);
       (new TextBox() :> Control);
       (new Label() :> Control) |]

let moreCtrls = 
    [| (new Button() :> Control);
       (new TextBox() :> Control) |]
       
let control = 
    let temp = moreCtrls.[0]
    temp.Text <- "Click me"
    temp
    
let button = 
    let temp = (control :?> Button)
    temp.DoubleClick.Add(fun e -> MessageBox.Show("Hey") |> ignore)
    temp

let anotherObj = ("Another string value." :> obj)

if (anotherObj :? string) then
    print_endline "This object is a string."
else
    print_endline "This object is not a string."

#light
open System.Windows.Forms

let showForm(form : Form) =
    form.Show()
    
// PrintPreviewDialog定义在BCL中，派生自Form类
let myForm = new PrintPreviewDialog()

showForm myForm

showForm(myForm :> Form)

let showFormRevised(form : #Form) =
    form.Show()
   
let myForm = new PrintPreviewDialog()

showFormRevised myForm

let myCtrls = 
    [| (new Button() :> Control);
       (new TextBox() :> Control);
       (new Label() :> Control) |]
       
let uc(c : #Control) = c :> Control
let myConciseCtrls =
    [| uc(new Button()); uc(new TextBox()); uc(new Label()) |]

使用记录类型模拟对象
#light
open System
open System.Drawing
open System.Windows.Forms

// 定义两个方法，此时仅仅声明函数的类型
type Shape =
    { reposition : Point -> unit;
      draw : Graphics -> unit }

// 创建一个Shape实例，并为它实现了两个方法  
let makeShape initPos draw =
    let currPos = ref initPos in
    {   reposition = (fun newPos -> currPos := newPos);
        draw = (fun g -> draw !currPos g);
    }
    
// 创建一个circle（Shape）实例，它替换了前面draw的实现
let makeCircle initPos diam =
    makeShape initPos (fun pos g ->
        g.DrawEllipse(Pens.Blue, pos.X, pos.Y, diam, diam))
    
// 创建一个square（Shape）实例，它替换了前面draw的实现   
let makeSquare initPos size =
    makeShape initPos (fun pos g ->
        g.DrawRectangle(Pens.Blue, pos.X, pos.Y, size, size))

let getPoint(x, y) = new Point(x, y)

let shapes =
    [ makeCircle (getPoint(10, 10)) 20; makeSquare (getPoint(30, 30)) 20; ]
    
let mainForm =
    let form = new Form()
    let rand = new Random()
    form.Paint.Add(fun e ->
        shapes |> List.iter(fun s -> s.draw e.Graphics)
    )
    form.Click.Add(fun e ->
        shapes |> List.iter(fun s -> 
            s.reposition(new Point(rand.Next(form.Width), rand.Next(form.Height)));
            form.Invalidate())
    )
    form

[<STAThread>]
do Application.Run(mainForm)

#light

// 包含两个字段，一个方法
type Point =
    {   mutable top : int;
        mutable left : int }
    with
        member this.Swap() =
            let temp = this.top
            this.top <- this.left
            this.left <- temp
    end
    
let printAnyNewline x =
    print_any x
    print_newline()

// 定义Point类的实例
let p = { top = 30; left = 40; }

let main() =
    printAnyNewline p
    p.Swap()
    printAnyNewline p
    
main()

{ top = 30;
 left = 40;}
{ top = 40;
 left = 30;}

#light

type DrinkAmount =
    | Coffee of int
    | Tea of int
    | Water of int
    with
        override this.ToString() =
            match this with
            | Coffee x -> Printf.sprintf "Coffee: %i" x
            | Tea x -> Printf.sprintf "Tea: %i" x
            | Water x -> Printf.sprintf "Water: %i" x
    end
    
let t = Tea 2
print_endline (t.ToString())

Tea: 2