Objective-C Memory Management with ARC - raywenderlich.com

ARC takes the pain and suffering out of memory management, and makes it - dare I say - easy in Objective-C.

----
About www.raywenderlich.com:

raywenderlich.com is a website focused on developing high quality programming tutorials. Our goal is to take the coolest and most challenging topics and make them easy for everyone to learn – so we can all make amazing apps.

We are also focused on developing a strong community. Our goal is to help each other reach our dreams through friendship and cooperation. As you can see below, a bunch of us have joined forces to make this happen: authors, editors, subject matter experts, app reviewers, and most importantly our amazing readers!

----

About Memory Management (from Apple)

https://developer.apple.com/library/content/releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html

Automatic Reference Counting (ARC) is a compiler feature that provides automatic memory management of Objective-C objects. Rather than having to think about retain and release operations, ARC allows you to concentrate on the interesting code, the object graphs, and the relationships between objects in your application.

ARC works by adding code at compile time to ensure that objects live as long as necessary, but no longer. Conceptually, it follows the same memory management conventions as manual reference counting (described in Advanced Memory Management Programming Guide) by adding the appropriate memory management calls for you.

In order for the compiler to generate correct code, ARC restricts the methods you can use and how you use toll-free bridging (see Toll-Free Bridged Types). ARC also introduces new lifetime qualifiers for object references and declared properties.

ARC is supported in Xcode 4.2 for OS X v10.6 and v10.7 (64-bit applications) and for iOS 4 and iOS 5. Weak references are not supported in OS X v10.6 and iOS 4.

Xcode provides a tool that automates the mechanical parts of the ARC conversion (such as removing retain and release calls) and helps you to fix issues the migrator can’t handle automatically (choose Edit \ Refactor \ Convert to Objective-C ARC). The migration tool converts all files in a project to use ARC. You can also choose to use ARC on a per-file basis if it’s more convenient for you to use manual reference counting for some files.

ARC Enforces New Rules
To work, ARC imposes some new rules that are not present when using other compiler modes. The rules are intended to provide a fully reliable memory management model; in some cases, they simply enforce best practice, in some others they simplify your code or are obvious corollaries of your not having to deal with memory management. If you violate these rules, you get an immediate compile-time error, not a subtle bug that may become apparent at runtime.

You cannot explicitly invoke dealloc, or implement or invoke retain, release, retainCount, or autorelease.
The prohibition extends to using @selector(retain), @selector(release), and so on.

You may implement a dealloc method if you need to manage resources other than releasing instance variables. You do not have to (indeed you cannot) release instance variables, but you may need to invoke systemClassInstance setDelegate:nil on system classes and other code that isn’t compiled using ARC.

Custom dealloc methods in ARC do not require a call to super dealloc (it actually results in a compiler error). The chaining to super is automated and enforced by the compiler.

You can still use CFRetain, CFRelease, and other related functions with Core Foundation-style objects (see Managing Toll-Free Bridging).

You cannot use NSAllocateObject or NSDeallocateObject.
You create objects using alloc; the runtime takes care of deallocating objects.

You cannot use object pointers in C structures.
Rather than using a struct, you can create an Objective-C class to manage the data instead.

There is no casual casting between id and void *.
You must use special casts that tell the compiler about object lifetime. You need to do this to cast between Objective-C objects and Core Foundation types that you pass as function arguments. For more details, see Managing Toll-Free Bridging.

You cannot use NSAutoreleasePool objects.
ARC provides @autoreleasepool blocks instead. These have an advantage of being more efficient than NSAutoreleasePool.

About Objective C (from Wikipedia)

Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. It was the main programming language used by Apple for the OS X and iOS operating systems, and their respective application programming interfaces (APIs) Cocoa and Cocoa Touch prior to the introduction of Swift.

The programming language Objective-C was originally developed in the early 1980s. It was selected as the main language used by NeXT for its NeXTSTEP operating system, from which OS X and iOS are derived.

Видео Objective-C Memory Management with ARC - raywenderlich.com канала raywenderlich.com