Obj-C ++:用于识别Objective-C类的模板元功能? [英] Obj-C++: template metafunction for recognizing Objective-C classes?

问题描述

使用Objective-C ++，如果且仅当T为Objective-C类时，我才能编写C ++ IsObjectiveCClass<T>模板元函数，使IsObjectiveCClass<T>::value为true吗?

Using Objective-C++, can I write a C++ IsObjectiveCClass<T> template metafunction such that IsObjectiveCClass<T>::value is true if and only if T is an Objective-C class?

从语言的C/C ++子集的角度来看，ObjC类到底是什么?当在C/C ++上下文中使用时，MyClass *指针的行为似乎与普通的C指针相同.这是否意味着MyClass也是C类型?

Exactly what are ObjC classes from the viewpoint of the C / C++ subset of the language? When used in a C / C++ context, MyClass* pointers seem to behave like ordinary C pointers; does that mean that MyClass is also a C type?

推荐答案

以下是一种简化的解决方案，该解决方案在大多数情况下(如果不是全部，有人可以想到这可能会失败吗?)(在xcode中使用clang 3.0) 4.2-对于早期的clang版本，请使用typedefs而不是使用别名):

Here is a simplistic solution that should work in most (if not all? Can anyone think of when this might fail?) cases (it uses clang 3.0 via xcode 4.2 - use typedefs instead of using aliases for earlier clang versions):

template<class T> struct IsObjectiveCClass 
{ 
  using yesT = char (&)[10];
  using noT = char (&)[1];
  static yesT choose(id);
  static noT choose(...);
  static T make();
  enum { value = sizeof(choose(make())) == sizeof(yesT) }; 

};

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