Delphi通用类可以从其类参数中下降吗？ [英] Can a Delphi generic class descend from its class argument?

问题描述

我一直在尝试定义一个通用的，可继承的TSingleton类。这是我正在进行的：

  TSingleton< RealClass，InheritsFrom：class> = class（InheritsFrom）
 strict private 
 class var FInstance：RealClass; 
 protected 
 procedure InstanceInitialization; virtual; 
 public 
析构函数Destroy;覆盖
类程序创建;重新引入
类函数实例：RealClass; 
类程序InstanceFree; 
结束
  

目标是能够将单例模式插入在继承树中。所以不要这样声明：

  TMySingletonComponent = class（TComponent）
 
 end; 
  

需要在那里实现单例模式，我会声明如下：

  TMyGenericSingletonComponent = class（TSingleton< TMyGenericSingletonComponent，TComponent>）
 end; 
  

可惜，这不行。我收到以下错误（D2010）：

  TSingleton< RealClass，InheritsFrom：class> = class（InheritsFrom）/// E2021需要类类型
  

现在我在想，德尔福XE？有没有一些干净的黑客可以用来在D2010做这项工作？有没有一些根本原因，为什么这不能工作？

解决方案

根据设计，你不能创建一个派生的泛型类从其中一个类型的参数。

I've been trying to define a generic, inheritable TSingleton class. Here's what I had in progress:

  TSingleton<RealClass, InheritsFrom : class> = class(InheritsFrom)
  strict private
    class var FInstance : RealClass;
  protected
    procedure InstanceInitialization;virtual;
  public
    destructor Destroy; override;
    class procedure Create; reintroduce;
    class function Instance : RealClass;
    class procedure InstanceFree;
  end;

The goal was to be able to "insert" the singleton pattern in an inheritance tree. so instead of declaring something like this :

  TMySingletonComponent = class(TComponent)

  end;

And need to implement the singleton pattern there, I would declare something like this :

  TMyGenericSingletonComponent = class(TSingleton<TMyGenericSingletonComponent,TComponent>)
  end;

Sadly, this won't work. I'm getting the following error(In D2010):

  TSingleton<RealClass, InheritsFrom : class> = class(InheritsFrom) ///E2021 Class type required

Now I was wondering, would this work in Delphi XE? Is there some "clean hack" I could use to make this work in D2010? Is there some fundamental reasons why this can't work?

解决方案

By design, you can't create a generic class which derives from one of its type arguments.

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