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:

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.