类声明之间的区别 [英] Differences between class declarations

问题描述

有许多方法可以声明一个新的类类型：

There are many ways to declare a new class type:

1. TMyClass1 = TObject;


2. TMyClass2 = type TObject;


3. = class end;


4. TMyClass4 = class（TObject）;


5. TMyClass5 = class（TObject）end;

1. TMyClass1 = TObject;
2. TMyClass2 = type TObject;
3. TMyClass3 = class end;
4. TMyClass4 = class(TObject);
5. TMyClass5 = class(TObject) end;

类3,4和5是 TObject 的后代，但不清楚1和2是如何不同的，3,4和5之间的区别是什么。

It's my understanding that class 3, 4 and 5 are descendants of TObject, but it's not clear how 1 and 2 differ, and what the differences between 3,4 and 5 are.

有任何差异吗？

推荐答案

• code> TMyClass1 只是一个别名 - TObject 的不同名称


• TMyClass2 是 TObject （我们称之为type'd types）的强类型化别名;它是非常不寻常的使用这个与类，虽然，通常你会使用这个与例如。 Pointer 创建一个句柄类型或某事（例如，如何在Windows.pas中使用它）。


• TMyClass3 是一个类，隐含地从 TObject 下降，没有新成员。


• TMyClass4 是一个类，显式地从 TObject 下降，没有新成员，使用简洁的语法。通常用于标记类，其中类本身的唯一性是有趣的事情 - 通常用于异常后代


• TMyClass5 是一个类，显式地从 TObject 下降，没有新成员。该声明中的 TObject 是多余的，但它不会对任何内容造成明显的损害。


• TMyClass1 is just an alias - a different name for TObject
• TMyClass2 is a strongly typed alias for TObject (we call them "type'd types"); it's very unusual to use this with classes, though, normally you'd use this with e.g. Pointer to create a handle type or something (see e.g. how this is used in Windows.pas).
• TMyClass3 is a class, implicitly descending from TObject, with no new members.
• TMyClass4 is a class, explicitly descending from TObject, with no new members, using the concise syntax. More normally, this is used for marker classes, where the uniqueness of the class itself is the interesting thing - often used for Exception descendants
• TMyClass5 is a class, explicitly descending from TObject, with no new members. The TObject in the declaration is redundant, but it doesn't harm anything to make it explicit.

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