以类型安全的方式将方法的代码作为参数传递 [英] Passing a method's code as an argument in a typesafe way

问题描述

将方法作为参数传递不是问题:

Passing a method as an argument is not a problem:

type
  TSomething = class
    Msg: string;
    procedure Show;
  end;

procedure TSomething.Show;
begin
  ShowMessage(Msg);
end;

type TProc = procedure of object;

procedure Test(Proc: TProc);
begin
  Proc;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  Smth: TSomething;

begin
  Smth:= TSomething.Create;
  Smth.Msg:= 'Hello';
  Test(Smth.Show);
end;

我需要一些棘手的事情 - 只传递方法的代码部分.我知道我可以做到:

I need something tricky - to pass only a code part of a method. I know I can do it:

procedure Test2(Code: Pointer);
var
  Smth: TSomething;
  Meth: TMethod;

begin
  Smth:= TSomething.Create;
  Smth.Msg:= 'Hello Hack';
  Meth.Data:= Smth;
  Meth.Code:= Code;
  TProc(Meth);
  Smth.Free;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  Test2(@TSomething.Show);
end;

但这是一个黑客和不安全的 - 编译器无法检查方法的参数.

but that is a hack and unsafe - the compiler can't check the method's arguments.

问题:是否可以以类型安全的方式做同样的事情?

The question: Is it possible to do the same in a typesafe way?

推荐答案

我终于明白了.带类型检查，无需为调用事件声明变量！

I got it finally. With type checking and no need to declare variable for the calling event!

type

  TSomething = class
    Msg: string;
    procedure Show;
    procedure ShowWithHeader(Header : String);
  end;

  TProc = procedure of object;
  TStringMethod = procedure(S : String) of Object;

procedure TSomething.Show;
begin
  ShowMessage(Msg);
end;

procedure TSomething.ShowWithHeader(Header: String);
begin
  ShowMessage(Header + ' : ' + Msg);
end;

procedure Test2(Code: TProc);
var
  Smth: TSomething;
begin
  Smth:= TSomething.Create;
  Smth.Msg:= 'Hello Hack 2';
  TMethod(Code).Data := Smth;
  Code;
  Smth.Free;
end;

procedure Test3(Code: TStringMethod; S : String);
var
  Smth: TSomething;
begin
  Smth:= TSomething.Create;
  Smth.Msg:= 'Hello Hack 3';
  TMethod(Code).Data := Smth;
  Code(S);
  Smth.Free;
end;

procedure TForm4.btn1Click(Sender: TObject);
begin
  Test2(TSomething(nil).Show);
//  Test2(TSomething(nil).ShowWithHeader); // Cannot Compile
end;

procedure TForm4.btn2Click(Sender: TObject);
begin
//  Test3(TSomething(nil).Show,'Hack Header');  // Cannot Compile
  Test3(TSomething(nil).ShowWithHeader,'Hack Header');
end;

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