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Editorial Team
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Asked: 2026-06-14T21:56:51+00:00

Sometimes I like to browse Apple source code to see how the pros do

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Sometimes I like to browse Apple source code to see how the pros do it, and sometimes learn a thing or two. I’m looking now at the header file for NSManagedObjectContext.h, and for their global variables, for say NSManagedObjectContextDidSaveNotification, they declare it like so:

COREDATA_EXTERN NSString * const NSManagedObjectContextDidSaveNotification;

whereas typically it would just be:

extern NSString * const NSManagedObjectContextDidSaveNotification

Cmd+clicking on COREDATA_EXTERN takes me to its definition:

#define COREDATA_EXTERN     extern

So COREDATA_EXTERN is just equal to extern, so my question is, why do they not just use extern?

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1 Answer

  1. Editorial Team

    If you check out the CoreDataDefines.h file, you’ll see a few different definitions for COREDATA_EXTERN, such as:

    #ifdef __cplusplus
#define COREDATA_EXTERN     extern "C"

    or:

    #ifdef __cplusplus
#define COREDATA_EXTERN     extern "C" _NSWINDOWS_DLL_GOOP

    This allows for some platform specific definitions, all contained under a single definition.

    Windows goop, that’s funny. What I’d like to know is when you would be compiling core data on a Windows platform….

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