通用类型标识符转换。如何？

发布于 2024-08-29 15:34:06 字数 639 浏览 8 评论 0原文

如何将 TypeIdenitifier 转换为类类型？我需要使用隐式转换。

type
  TMyChildArray<T>=class(TMyArray<T>)
    private
      FData:Array of T;
      procedure AddEnd();
  end;

  TTypeIdenitifierParentClass=class(TAnotherParentClass)
    protected
      TestField:Cardinal;
  end;


  procedure TMyChildArray<T>.AddEnd();
  var elem:T;
  begin
    for elem in Fdata do
      TTypeIdenitifierParentClass(elem).TestField:=0;
  end;

我在隐式转换“TTypeIdenitifierParentClass(elem).TestField:=0;”上得到“无效类型转换”。

我想要使用的原则是 TypeIdenitifier 将表示一个从 TTypeIdenitifierParentClass 派生的类。类类型有很多，但它们都派生于该类。

我该怎么做？

原文

How do I convert the TypeIdenitifier to a class type? I need to use implicit convertion.

type
  TMyChildArray<T>=class(TMyArray<T>)
    private
      FData:Array of T;
      procedure AddEnd();
  end;

  TTypeIdenitifierParentClass=class(TAnotherParentClass)
    protected
      TestField:Cardinal;
  end;


  procedure TMyChildArray<T>.AddEnd();
  var elem:T;
  begin
    for elem in Fdata do
      TTypeIdenitifierParentClass(elem).TestField:=0;
  end;

I get "Invalid typecast" on the implicit convertion "TTypeIdenitifierParentClass(elem).TestField:=0;".

The principle I want to use is that the TypeIdenitifier will represent a class that descends from TTypeIdenitifierParentClass.There are many class types,but all of them descend that class.

How do I do this?

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花开柳相依 2024-09-05 15:34:06

delphi 抱怨转换的原因是编译器无法知道 T 是否可以类型转换为“TTypeIdenitifierParentClass”。您需要将 T 限制为从“TTypeIdenitifierParentClass”降序的类

尝试以下操作

type
  TTypeIdenitifierParentClass=class(TAnotherParentClass)
    protected
      TestField:Cardinal;
  end;

  TMyChildArray<T: TTypeIdenitifierParentClass>=class(TMyArray<T>)
    private
      FData:Array of T;
      procedure AddEnd();
  end;

  procedure TMyChildArray<T>.AddEnd();
  var elem:T;
  begin
    for elem in Fdata do
      elem.TestField:=0;
  end;

The reason delphi is complaining about the cast is because the compiler has no way of knowing if T can be type casted to "TTypeIdenitifierParentClass". You need to limit T to classes descending from "TTypeIdenitifierParentClass"

Try the following

type
  TTypeIdenitifierParentClass=class(TAnotherParentClass)
    protected
      TestField:Cardinal;
  end;

  TMyChildArray<T: TTypeIdenitifierParentClass>=class(TMyArray<T>)
    private
      FData:Array of T;
      procedure AddEnd();
  end;

  procedure TMyChildArray<T>.AddEnd();
  var elem:T;
  begin
    for elem in Fdata do
      elem.TestField:=0;
  end;

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