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Are classes structs or struct pointer

If I'm not mistaken, do structs mean objects, and pointers to a structure mean a pointer to objects to the right? The article says that classes are structures, which means that they are objects.

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The traditional definition of a class in Objective-C looks like this:

struct objc_class {
    Class isa;
    Class super_class;
    const char *name;
    long version;
    long info;
    long instance_size;
    struct objc_ivar_list *ivars;
    struct objc_method_list **methodLists;
    struct objc_cache *cache;
    struct objc_protocol_list *protocols;
    };

So, if he says that classes are structures, then how will they correspond to an argument objc_msgSend(id self, SEL_cmd)that requires a structure pointer that has a type id?

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2 answers

Classes are structures, but Classa pointer type, which is defined as

typedef struct objc_class *Class;

and this answers the first part of the question.

Now, if you look <objc/objc.h>, you will find

struct objc_class {
    Class isa  OBJC_ISA_AVAILABILITY;

 #if !__OBJC2__
    Class super_class                                        OBJC2_UNAVAILABLE;
    const char *name                                         OBJC2_UNAVAILABLE;
    long version                                             OBJC2_UNAVAILABLE;
    long info                                                OBJC2_UNAVAILABLE;
    long instance_size                                       OBJC2_UNAVAILABLE;
    struct objc_ivar_list *ivars                             OBJC2_UNAVAILABLE;
    struct objc_method_list **methodLists                    OBJC2_UNAVAILABLE;
    struct objc_cache *cache                                 OBJC2_UNAVAILABLE;
    struct objc_protocol_list *protocols                     OBJC2_UNAVAILABLE;
#endif

} OBJC2_UNAVAILABLE;

<obj/runtime.h>

/// Represents an instance of a class.
struct objc_object {
    Class isa  OBJC_ISA_AVAILABILITY;
};

, Objective-C 2.0 objc_object objc_class , isa.

Class, id: - .

, , -, Obj-C . .

- clang:

ASTContext.cpp Class

TypedefDecl *ASTContext::getObjCClassDecl() const {
  if (!ObjCClassDecl) {
    QualType T = getObjCObjectType(ObjCBuiltinClassTy, 0, 0);
    T = getObjCObjectPointerType(T);
    TypeSourceInfo *ClassInfo = getTrivialTypeSourceInfo(T);
    ObjCClassDecl = TypedefDecl::Create(const_cast<ASTContext &>(*this),
                                        getTranslationUnitDecl(),
                                        SourceLocation(), SourceLocation(),
                                        &Idents.get("Class"), ClassInfo);
  }

  return ObjCClassDecl;
}

id

TypedefDecl *ASTContext::getObjCIdDecl() const {
  if (!ObjCIdDecl) {
    QualType T = getObjCObjectType(ObjCBuiltinIdTy, 0, 0);
    T = getObjCObjectPointerType(T);
    TypeSourceInfo *IdInfo = getTrivialTypeSourceInfo(T);
    ObjCIdDecl = TypedefDecl::Create(const_cast<ASTContext &>(*this),
                                     getTranslationUnitDecl(),
                                     SourceLocation(), SourceLocation(),
                                     &Idents.get("id"), IdInfo);
  }

  return ObjCIdDecl;
}

getObjCObjectPointerType. Class, id Objective-C.

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, structs , struct ?

, . Objective-C ( ) , "" " " .

, , , objc_msgSend()?

, . Class typedef struct objc_class *, id typedef struct objc_object *. () , isa, , , .

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