Program entry with main Header imports with #import NSString literals NSNumber boxing Scalar numeric types BOOL and YES/NO Format specifiers in NSLog Automatic type inference with __auto_type C structs inside Objective-C Preprocessor conditionals

NSObject subclasses Instance methods Class methods Message sending syntax Properties and dot syntax Custom initializers Designated initializer pattern Class extensions Categories Selectors with @selector

ARC strong references Weak references Copy properties Autorelease pools Retain cycles Weak-strong dance Bridging Core Foundation objects Dealloc cleanup Object lifetime in blocks Unsafe unretained references

NSArray creation NSMutableArray mutation NSDictionary key-value storage NSMutableDictionary updates NSSet uniqueness NSOrderedSet ordering Fast enumeration NSEnumerator traversal NSNull placeholders Collection filtering with predicates

Declaring protocols Protocol conformance Optional protocol methods id dynamic type instancetype return type Lightweight generics Nullability annotations Runtime type checks respondsToSelector Key-value coding

Block literals Capturing local variables __block mutable captures Blocks as callbacks Block properties Dispatch queues dispatch_async dispatch_after Dispatch groups Dispatch semaphores

Reading text files Writing text files NSURL construction NSURLComponents query items NSData bytes NSJSONSerialization encoding NSJSONSerialization decoding NSUserDefaults storage NSNotificationCenter observers NSError error reporting

NSError out parameters NSAssert preconditions XCTest assertions Objective-C exceptions C function interoperability Objective-C++ bridge files Availability checks NS_SWIFT_NAME annotation Debug descriptions Compiler warnings as errors