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: