什么是Objective-C“类继承”？ [英] What is an Objective-C "class continuation"?

问题描述

我无法完全明白我所看到的 Objective-C 类继承。是/这些...

1. 在 @implementation （ .m ）文件？


2. 类类别的另一个名称？ （不太可能， ASFAIK 类别不能有Ivars，期间）


3. 类别额外资讯的另一个名称？

1. 这是一个ARC特有的功能吗？


2. 是否有特定的运行时或其他使用要求？


3. 这是创建 @property ，以及？为什么会比设置 @interface 文件/声明更好地设置ivars或属性？


4. 人们通过使用这样的特定术语来复杂化讨论 - 这似乎不存在于任何官方文档中（我可以找到）。

在Objective-C中，在头文件中定义东西（比如一个属性）而不是.m文件之间的区别？
讨论涉及这个问题，但只是云问题进一步 - 或至少失败

解决方案

继承类是Apple称为 类扩展 。我已经看到铛叫他们继续类和gcc使用类继承。

在clang或gcc中编译：

  @interface Foo：NSObject 
 @property int a; 
 @end 
 
 @interface Foo（）
 @property float a; 
 @end 
  

...你会得到有趣的名字的错误。 p>

要回答您的问题的其余部分：

1. 这样的事件的范围，生命周期和用例是什么？

扩展用于声明类的私有接口。您还可以使用它来重新声明（细化）公共属性声明。

2. 特定于ARC的功能？

否。

3. 是否有特定的运行时间或其他要求？

类扩展是一个编译时概念，不需要特殊的运行时。当然，他们需要一个支持它们的编译器（clang和gcc做在当前版本中）。

4. 这是一个创建@property的合适地方吗？为什么会比设置@interface文件/声明更好地设置ivars或属性？

是的。

5. 为什么人们使用这种特定的术语 - 似乎不存在于任何官方文档中（我可以找到）？

好吧，你知道...我也喜欢整个世界讲英语，但是暂时我很高兴我必须在学校学习它。

I can't quite figure out what I have seen referred to as an Objective-C "class continuation". Is this / are these…

1. Ivar(s) declared in the @implementation (.m) file?
2. Another name for a class category? (Unlikely, ASFAIK categories cannot have Ivars, period)
3. Another name for a class extension?
4. Something else?

That said...

1. What is the scope, lifetime, and usage case for such a thing?
2. Is this an ARC-specific "feature"?
3. Are there specific runtime, or other requirements for their use?
4. Is this an appropriate place to create an @property, as well? And why would this be a better place for setting ivars or properties than, say, the @interface file / declaration?
5. Why do people complicate discussions by using such specific terminology - that seems NOT to exist in any official documentation (that I could find)?

In question In Objective-C what is the difference between defining something (say a property) in the header file as opposed to the .m file? the discussion touches on this issue, but sort of just clouds the issue further - or at least fails to provide a canonical reference / definition of the term… hence this question.

解决方案

A continuation class is what Apple calls a class extension. I have seen clang call them "continuation class" and gcc uses "class continuation".

Compile this in clang or gcc:

@interface Foo : NSObject
@property int a;
@end

@interface Foo()
@property float a;
@end

... and you will get errors with the funny names.

To answer the rest of your question:

1. What is the scope, lifetime, and usage case for such a thing?

Extensions are used to declare the private interface for a class. You can also use it to redeclare (refine) public property declarations.

2. Is this an ARC-specific "feature"?

NO.

3. Are there specific runtime, or other requirements for their use?

Class Extensions are a compile time concept and do not require a special runtime. Of course they do require a compiler that supports them (both clang and gcc do in current versions).

4. Is this an appropriate place to create an @property, as well? And why would this be a better place for setting ivars or properties than, say, the @interface file / declaration?

YES. Because you might want to have private properties.

5. Why do people complicate discussions by using such specific terminology - that seems NOT to exist in any official documentation (that I could find)?

Well, you know... I'd also prefer if the whole world spoke English, but for the time being I'm happy with the fact that I had to learn it in school.

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