We were a bit hard on Core Data last week, so for this issue of NSHipster, we bring you a guided tour of the best open source libraries for working with Core Data. Read on to see how you might make the most from your Core Data experience.

Among the most important architectural decisions made when building an app is how to persist data between launches. The question of how, exactly, to re-create the state of the app from the time it was last opened; of how to describe the object graph in such a way that it can be flawlessly reconstructed next time.

GPUImage is a BSD-licensed iOS library that lets you apply GPU-accelerated filters and other effects to images, live camera video, and movies. If you're not careful, you may well end up creating a camera app by the end of the article.

In all of the hubbub of torch burning and pitchfork raising, you may have completely missed a slew of additions to MapKit in iOS 6.1.

Test your knowledge of general programming knowledge, Cocoa APIs, and Apple trivia in this first-ever NSHipster Quiz. How NSHip are you?

A short post for this week: everything you need to know about NSSecureCoding.

Once again, encoding our logical universe into the cold, calculating bytecode of computers forces us to deal with these questions one way or another. And as you'll see from our discussion of boolean types in Objective-C and its kin, truth is indeed stranger than fiction.

Perhaps what Apple is most renowned for is its consistent track record for creating great webservices. From consumer products like MobileMe and Ping to developer tools including the Provisioning Portal and iTunes Connect, Apple has continued to set new standards for convenience, robustness, and extensibility.

Search Kit is a C framework for searching and indexing content in human languages. It supports matching on phrase or partial word, including logical & wildcard operators, and can rank results by relevance. Search Kit also provides document summarization, which is useful for generating representative excerpts. And best of all: it's thread-safe.

In C, the scope and lifetime of a variable or function within a program is determined by its storage class. Understanding these storage classes allows us to decipher common incantations found throughout Objective-C

UIAppearance allows the appearance of views and controls to be consistently defined across the entire application.

Back Row is a private framework used in the Apple TV user experience. Rather than waiting for Apple to open up the Apple TV SDK, one can take matters into their own hands.

"When at first you don't succeed, use an object-oriented injection point to override default exception handling." This is the sort of advice you would have learned at mother's knee if you were raised by NSAssertionHandler.

Breaking from a tradition of covering Apple APIs exclusively, this edition of NSHipster will look at an open source project that exemplifies a brave new era of open source contribution to Objective-C: ReactiveCocoa.

NSURLCache provides a composite in-memory and on-disk caching mechanism for URL requests to your application. As part of Foundation's URL Loading System, any request loaded through NSURLConnection will be handled by NSURLCache.

From number stations and numerology to hieroglyphics and hobo codes, there is something truly fascinating about finding meaning that hides in plain sight. Though hidden messages in and of themselves are rarely useful or particularly interesting, it's the thrill of the hunt that piques our deepest curiosities.

Boxing is the process of encapsulating scalars and value types with an object container, and is primarily used to store those values in collection objects—namely arrays and dictionaries. In Foundation, the reigning featherweight champion of boxing is NSValue.

Strings are perhaps the most versatile data type in computing. They're passed around as symbols, used to encode numeric values, associate values to keys, represent resource paths, store linguistic content, and format information. Having a strong handle on user-facing strings is essential to making a great user experience.

A recurring theme of this publication has been the importance of a healthy relationship with the compiler. Like any craft, one's effectiveness as a practitioner is contingent on how they treat their tools. Take good care of them, and they'll take good care of you.

Understanding the concept of nothingness is as much a philosophical issue as it is a pragmatic one. We are inhabitants of a universe of somethings, yet reason in a logical universe of existential uncertainties. As a physical manifestation of a logical system, computers are faced with the intractable problem of how to represent nothing with something.

In celebration of the forthcoming `year++`, I thought it'd be fun to compile a list of some of your favorite tips and tricks of the trade. Readers were asked to submit their favorite piece of Objective-C trivia, framework arcana, hidden Xcode feature, or anything else they thought is cool.

Unless you were a Math Geek or an Ancient Greek, Geometry was probably not your favorite subject in high school. No, chances are that you were that kid in class who dutifully programmed all of the necessary formulæ into your TI-8X calculator. Keeping in the tradition of doing the least amount of math possible, here are some semi-obscure CoreGraphics functions to make your job easier.

Objective-C is a rapidly evolving language, in a way that you just don't see in established programming languages. Developments range from the mundane to paradigm-changing, but telling the difference takes practice. Because we're talking about low-level language features, it's difficult to understand what implications they may have higher up with API design.

Rubyists laugh at Objective-C’s bloated syntax. Although we lost a few pounds over the summer with our sleek new object literals, those Red-headed bullies still taunt us with their map one-liners and their fancy Symbol#to_proc. Fortunately, Key-Value Coding has an ace up its sleeves.

Why isn't `NSOrderedSet` a subclass of `NSSet`? The answer may surprise you.

A skilled Objective-C developer is able to gracefully switch between Objective and Procedural paradigms, and use each to their own advantage.

Of all the Foundation classes, NSValueTransformer is perhaps the one that fared the worst in the shift from OS X to iOS. But you know what? It's ripe for a comeback. With a little bit of re-tooling and some recontextualization, this blast from the past could be the next big thing in your application.

Foundation’s URL Loading System is something that every iOS developer would do well to buddy up with. And of all of networking classes and protocols of Foundation, NSURLProtocol is perhaps the most obscure and powerful.

UITableView starts to become unwieldy once it gets to a few hundred rows. If users are reduced to frantically scratching at the screen like a cat playing Fruit Ninja in order to get at what they want… you may want to rethink your UI approach.

NSLinguisticTagger is a veritable Swiss Army Knife of linguistic functionality, with the ability to tokenize natural language strings into words, determine their part-of-speech & stem, extract names of people, places, & organizations, and tell you the languages & respective writing system used in the string.

Address Book UI is an iOS framework for displaying, selecting, editing, and creating contacts in a user's Address Book. Similar to the Message UI framework, Address Book UI contains a number of controllers that can be presented modally, to provide common system functionality in a uniform interface.

If we were to go code-watching for Objective-C, what would we look for? Square brackets, ridiculously-long method names, and @'s. "at" sign compiler directives are as central to understanding Objective-C's gestalt as its ancestry and underlying mechanisms. It's the sugary glue that allows Objective-C to be such a powerful, expressive language, and yet still compile all the way down to C.

#pragma declarations are a mark of craftsmanship in Objective-C. Although originally purposed for compiling source code across many different compilers, the modern Xcode-savvy programmer uses #pragma declarations to very different ends.

UICollectionView single-handedly changes the way we will design and develop iOS apps from here on out. This is not to say that collection views are in any way unknown or obscure. But being an NSHipster isn't just about knowing obscure gems in the rough. Sometimes, it's about knowing about up-and-comers before they become popular and sell out.

Foundation boasts one of the best, most complete implementations of strings around. But a string implementation is only as good as the programmer who wields it. So this week, we're going to explore some common uses--and misuses--of an important part of the Foundation string ecosystem: NSCharacterSet.

Accessibility, like internationalization, is one of those topics that's difficult to get developers excited about. But as you know, NSHipster is all about getting developers excited about this kind of stuff.

Internationalization is like flossing: everyone knows they should do it, but probably don't.

In the pantheon of collection data types in computer science, bag doesn't really have the same clout as lists, sets, associative arrays, trees, graphs, or priority queues. In fact, it's pretty obscure. You've probably never heard of it.

Everyone knows that the secret to making an app snappy and responsive is to offload computation to be done asynchronously in the background. Thus, the modern Objective-C developer has two options: Grand Central Dispatch or NSOperation.

Even for a blog dedicated to obscure APIs, NSIncrementalStore sets a new standard. It was introduced in iOS 5, with no more fanfare than the requisite entry in the SDK changelog. Ironically, it is arguably the most important thing to come out of iOS 5, which will completely change the way we build apps from here on out.

NSString is the crown jewel of Foundation. But as powerful as it is, we would be remiss no to mention its toll-free bridged cousin, CFMutableString. Or more specifically, CFStringTransform.

NSDateComponents serves an important role in the date and time APIs in Foundation. By itself, it's just a container for information about a date, such as its month, year, day of month, week of year, or whether that month is a leap month. Combined with NSCalendar, NSDateComponents becomes a remarkably convenient interchange format for calendar calculations.

Sorting: the old mainstay of the exams of an intro CS class and whiteboards of an entry-level programming interview. When was the last time you really needed to know how to implement Quicksort anyway?

Poor NSCache, always being overshadowed by NSMutableDictionary. It's as if no one knew it was there, ready to provide all of that garbage collection behavior that developers take great pains to re-implement themselves.

NSIndexSet (and its mutable counterpart, NSMutableIndexSet) represents a sorted collection of unique unsigned integers--think of it like an NSRange that supports non-contiguous series. It has wicked fast operations to find indexes in ranges or set intersections, and all of the convenience methods you'd expect in a Foundation collection class.