D- 泛型练习 ，继承，方法

unit Unit3;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls,System.Generics.Collections;

type
  TForm3 = class(TForm)
    btn1: TButton;
    procedure btn1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
  THttpResult<T: TStrings, constructor> = class   //限定T 为某个类型，
  private
    fIsSucc: Boolean;
    fData: T;
    fMsg: string;
    fUrl: string;
    fParamStr: string;
  public
  end;
  ThttpResultA =class(THttpResult<TStrings>)
  end;
  ThttpResults =class(THttpResult<TStringList>)
  end;
  A<T> =class
  end;
  AA<T> =class(A<T>) //AA=class(A<T>) 这样写会提示说为定义T
  end;
  B=class(A<ThttpResultA>) //B=class(A<int>)  这里会错误， B<T>=class(A<int>)这样不错
  end;
  C<B>=class(A<ThttpResultA>) //这里的B并不是B类，而是一个没有任何意义的 占位符
  end;
  D<T>=class(A<ThttpResultA>) //这里的B并不是B类，而是一个没有任何意义的 占位符
  private
    fIsSucc :Boolean;
  public
    function QueryData<B>(url:string):string;
    function QueryData2<T>(url:string):string; //QueryData<T>(url:string):string; 这样会被认为和上一个函数相同
  end;
  TGQlist<T> = class(TList<T>)  //包含System.Generics.Collections,   TGQlist= class(TList<T>) 这样写是错误的
  end;
var
  Form3: TForm3;

implementation

{$R *.dfm}

procedure TForm3.btn1Click(Sender: TObject);
var
  temp :TStringList;
  temp2 :A<string>;   //可以这么用法。
begin
  temp2 := A<string>.Create;  //创建类
end;

{ D<T> }

function D<T>.QueryData<B>(url: string): string;
begin
  //
end;

function D<T>.QueryData2<T>(url: string): string;
begin

end;

end.