Backwards compatible macros for Objective-C nullability annotations and generics

Xcode7Macros.h

/**
 * The following preprocessor macros can be used to adopt the new nullability annotations and generics
 * features available in Xcode 7, while maintaining backwards compatibility with earlier versions of
 * Xcode that do not support these features.
 */

#if __has_feature(nullability)
#   define __ASSUME_NONNULL_BEGIN      NS_ASSUME_NONNULL_BEGIN
#   define __ASSUME_NONNULL_END        NS_ASSUME_NONNULL_END
#   define __NULLABLE                  nullable
#else
#   define __ASSUME_NONNULL_BEGIN
#   define __ASSUME_NONNULL_END
#   define __NULLABLE
#endif

#if __has_feature(objc_generics)
#   define __GENERICS(class, ...)      class<__VA_ARGS__>
#   define __GENERICS_TYPE(type)       type
#else
#   define __GENERICS(class, ...)      class
#   define __GENERICS_TYPE(type)       id
#endif

Xcode7MacrosExamples.h

/**
 * Here are some examples of the above macros being used.
 * The comments below each line represent the output of the preprocessor (e.g. what the compiler will see)
 * when using both Xcode 7 and Xcode 6.
 */

#import "Xcode7Macros.h"

__ASSUME_NONNULL_BEGIN
// Xcode 7: NS_ASSUME_NONNULL_BEGIN
// Xcode 6:
 
@interface __GENERICS(MyClass, GenericType1, GenericType2) : NSObject
// Xcode 7: @interface MyClass<GenericType1, GenericType2> : NSObject
// Xcode 6: @interface MyClass : NSObject

@property (nonatomic, strong) __GENERICS(NSArray, __GENERICS(NSDictionary, GenericType1, GenericType2) *) *arrayOfDictionaries;
// Xcode 7: @property (nonatomic, strong) NSArray<NSDictionary<GenericType1, GenericType2> *> *arrayOfDictionaries;
// Xcode 6: @property (nonatomic, strong) NSArray *arrayOfDictionaries;

- (__NULLABLE __GENERICS_TYPE(GenericType2))someMethodWithAParameter:(__NULLABLE NSString *)param;
// Xcode 7: - (nullable GenericType2)someMethodWithAParameter:(nullable NSString *)param;
// Xcode 6: - (id)someMethodWithAParameter:(NSString *)param;

@end
 
__ASSUME_NONNULL_END
// Xcode 7: NS_ASSUME_NONNULL_END
// Xcode 6:

@mickeyreiss Yes, __nullable is necessary for some C-like APIs, so defining another macro for it like you did may be required.
Also, the reason for the __ prefix in front of all these macros is to protect them a bit, since these are going to have to live in a public header that gets imported by clients of your library, but your clients probably don't want these macros showing up in the global (autocomplete) namespace.

What about value type definitions for NSArray or key value types for NSDictionary that are only available for Xcode 7? Do you have any idea?

e.g.:

// Xcode 6
NSArray *authParams; //<-- will produce AnyObject

// Xcode 7
NSArray<NSURLQueryItem *> *authParams;

Using __apple_build_version__ for the check? What do you think?

// http://en.wikipedia.org/wiki/Xcode#Toolchain_Versions
if defined(__apple_build_version__)
     if __apple_build_version__ >= 700059

@ricardopereira I'm not sure what you're asking here.

I want to support NSArray *authParams and NSArray<NSURLQueryItem *> *authParams. Any thoughts? /cc @bdash @mickeyreiss

@ricardopereira and why doesn't this work for you?

__GENERICS(NSArray, NSURLQueryItem *) *authParams;

Oh, sorry. Didn't know.
Thanks.

Xcode inserts automatically code such as

saveOperation.modifyRecordsCompletionBlock = 
^(NSArray <CKRecord *> * _Nullable savedRecords,
  NSArray <CKRecordID *> * _Nullable deletedRecordIDs,
  NSError * _Nullable operationErro) {...};

which fails at being compiled with Xcode 6, because of NSArray <CKRecord *> *. Is it possible to help Xcode 6 compiling?

@colasjojo You can probably just omit (delete) the _Nullable and <CKRecord *>/<CKRecordID *> entirely and it should continue to compile fine on Xcode 7 with no change in behavior. If you want to preserve the type information then you should try converting the syntax to use the macros in this gist, something like:

saveOperation.modifyRecordsCompletionBlock = 
^(__GENERICS(NSArray, CKRecord *) * _Nullable savedRecords,
  __GENERICS(NSArray, CKRecordID *) * _Nullable deletedRecordIDs,
  NSError * _Nullable operationErro) {...};

(You would need to also define a new macro for _Nullable and substitute that if you're trying to support Xcode 6.2 and earlier.)

@smileyborg I believe the macro breaks bridging into swift?

@samjarman They shouldn't, these are being used by projects that bridge to Swift. Are you seeing a specific issue?

Very cool, do you have a license for your code that we can use?
Thank you.