xcode 目标 c 中的轻量级泛型
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lightweight generics in objective c
提问by Hai Feng Kao
I am trying to implement the stack class with the lightweight generic.
But the code failed to compile because Xcode cannot find the definition of ObjectType
我正在尝试使用轻量级泛型实现堆栈类。但是代码编译失败，因为Xcode找不到ObjectType
@implementation Stack
- (ObjectType)popObject !!!!!!!!!Expected a type
{
return self.allObjects.firstObject;
}
@end
It's strange because the header declaration doesn't generate any errors.
这很奇怪，因为标头声明不会产生任何错误。
@interface Stack<__covariant ObjectType> : NSObject
- (ObjectType)popObject;
@property (nonatomic, readonly) NSArray<ObjectType> *allObjects;
@end
I could make it work by changing ObjectTypeto id.
Are there better way to fix the error?
我可以通过更改ObjectType为id. 有没有更好的方法来修复错误？
回答by Douglas Hill
Objective-C generics really are lightweight, and were added to improve interoperability with Swift, not to make Objective-C code safer. Similar to nullability, think of generics as a way to annotate your interface rather than a reason to change your implementation.
Objective-C 泛型确实是轻量级的，添加它是为了提高与 Swift 的互操作性，而不是为了使 Objective-C 代码更安全。与可空性类似，将泛型视为注释接口的一种方式，而不是更改实现的理由。
Changing ObjectTypeto idin the implementationis the best way forward.
在实现中更改ObjectType为是最好的前进方式。id
Further reading: article on Objective C Generics. Read bob's comment on that article if you want to know about __covariant.
进一步阅读：关于 Objective C 泛型的文章。如果您想了解有关__covariant.
回答by Sergii Martynenko Jr
Only a presumption, but, if replacing ObjectTypewith idworks, maybe you're using not a pointer type?
只有一个假设，但如果更换ObjectType用id的作品，也许你正在使用不是指针类型？
I mean, if you have @interface ObjectTypesomewhere, than in your Stackit should be ObjectType*both in <...>braces and in method return type
我的意思是，如果你有@interface ObjectType某个地方，Stack那么它应该ObjectType*在<...>大括号和方法返回类型中
If it's not an issue, sorry for misleading
如果不是问题，抱歉误导
