From Mattt Thompson, the creator of NSHipster.com and author of NSHipster: Obscure Topics in Objective-C, comes a new book about low-level programming on iOS & Mac OS X.
Perfect for intermediate and expert developers wanting to take a deeper dive into advanced topics, CFHipsterRef: Low-Level Programming on iOS & Mac OS X covers the core technologies powering Cocoa, Objective-C, and the operating system itself, including:
Kernel Objective-C Runtime Clang OSAtomic Grand Central Dispatch Inter-Process Communication CoreServices ImageI/O Accelerate Security SystemConfiguration International Components for Unicode DictionaryServices Xcode Toolchain Third-Party Tools CocoaPods
Good as a quick reference to study what is possible on a low-level. Certainly is not a complete guide or tutorial on how to do something (don't expect that).