What is arc in Objective-C?
This article is about a specific implementation of a language feature. For the general technology, see Reference counting. Automatic Reference Counting ( ARC) is a memory management feature of the Clang compiler providing automatic reference counting for the Objective-C and Swift programming languages.
What is arc in Swift?
Swift uses ARC to be predictable and efficient in resource-constrained environments. ARC works automatically, so you don’t need to participate in reference counting, but you do need to consider relationships between objects to avoid memory leaks. This is an important requirement that is often overlooked by new developers. How ARC works.
What does arc stand for?
Automatic Reference Counting ( ARC) is a memory management feature of the Clang compiler providing automatic reference counting for the Objective-C and Swift programming languages.
What is Xcode used for?
Xcode is Apple's integrated development environment (IDE) for macOS, used to develop software for macOS, iOS, iPadOS, watchOS, and tvOS.It was first released in 2003; the latest stable release is version 13.0, released on September 20, 2021, and is available via the Mac App Store free of charge for macOS Big Sur users.
What is ARC in iOS Swift?
Swift uses Automatic Reference Counting (ARC) to track and manage your app's memory usage. In most cases, this means that memory management “just works” in Swift, and you don't need to think about memory management yourself.
Is ARC a garbage collector?
Automatic Reference Counting is technically a form of garbage collection. However, typically when one refers to a garbage collector, they mean a separate process or subsystem that runs in the background independent of your application. ARC, on the other hand, is fully part of your application code.
What is ARC and MRC in Swift?
ARC is abbreviation of Automatic Reference Counting, and MRC is abbreviation of Manual Refetence Counting.
Is ARC runtime or compile time?
ARC is a compiler feature that provides automatic memory management of Objective-C objects. Instead of you having to remember when to use retain, release, and autorelease, ARC evaluates the lifetime requirements of your objects and automatically inserts appropriate memory management calls for you at compile time.
When was ARC introduced in iOS?
2011Apple introduced ARC in 2011 along with Max OS X Lion and iOS 5.
Is ARC a GC?
ARC differs from tracing garbage collection in that there is no background process that deallocates the objects asynchronously at runtime. Unlike tracing garbage collection, ARC does not handle reference cycles automatically.
What is ARC in Swift interview questions?
ARC/Automatic Reference Counting is a compile time feature for memory management in iOS. While using ARC, it only deallocate the memory for the objects when there are zero strong references to them.
What is MRC in memory management?
The Memory Reference Code (or MRC) is a fundamental component in the design of some computers, and is "one of the most important aspects of the BIOS" for an Intel-based motherboard.
What is heap memory iOS?
Take control of your app's GPU memory management by creating a large memory allocation for various buffers, textures, and other resources.
How is ARC implemented?
The mechanism of ARC is implemented in a library called Swift Runtime. It implements such core features as the runtime type system, including dynamic casting, generics, and protocol conformance registration [3]. Swift Runtime represents every dynamically allocated object with HeapObject struct.
What is weak in iOS Swift?
Swift Weak Reference As mentioned earlier, a weak reference doesn't protect the object from being deallocated. This is because when we declare a property as weak, the reference count of that property will never be more than 1. Here, we have used the weak keyword to denote colleague as the weak property.
What is difference between weak and strong in Swift?
In Swift, strong references are the default, so to make a reference weak you can use the weak keyword. Unlike strong references, a weak reference does not affect an instance's retain count. It does not hold onto the object. Before we dive into an example, let's briefly discuss why we have weak references at all.
What is the difference between ARC automatic reference counting and GC garbage collection?
Both GC (Garbage Collection) and ARC aim to take burden from the developer so that they need not worry about the reference count, when they should free objects, etc. GC is used in programming languages like Java, C#, Go and other scripting languages and ARC is used in Objective-C and Swift languages.
Is reference counting garbage collection?
Reference counting. Reference counting garbage collection is where each object has a count of the number of references to it. Garbage is identified by having a reference count of zero. An object's reference count is incremented when a reference to it is created, and decremented when a reference is destroyed.
Does Swift have garbage collection?
Many programming languages use garbage collection to collect unused memory, whereas swift uses ARC. ARC is technically a form of Garbage collection.
What is reference counting in compiler design?
Reference counting allows clients of your library to keep reference objects created by your library on the heap and allows you to keep track of how many references are still active.
What is ARC and how does it work in Swift?
Unlike other programming languages like Java or Kotlin, Swift doesn’t have a garbage collector. Instead, it uses a much faster technique called Automatic Reference Counting (ARC).
How does ARC know if it can free the memory used by a class instance?
Very simple: ARC will count how many properties, constants or variables point to that given instance.
Hands-on the keyboard: Xcode
Let’s suppose you have a class Author which represents the writer of a book.
Conclusion
Although Swift doesn’t have a garbage collector, it uses another technique called ARC. It consists of counting the number of strong references pointing to a specific instance.
Turn off ARC settings
When creating a project, there is a check box asking whether to use ARC. After creation, you can set Objective-C Automatic Reference Count to NO in Apple LLVM compiler 3.1-Language located below in Project Build Setting.
Development of a module that supports both activation and deactivation of ARC
If the ARC function is set to YES, the relase method is no longer available, so it is desirable to develop it so that it can be used regardless of active or inactive when creating libraries, etc. You can develop a module that supports both activation and deactivation of ARC using a preprocessor as shown below. Reference URL: http://www.learn-cocos2d.com/2011/11/everything-know-about-arc/.
Can you manually send retain/release/autorelease in ARC?
ARC not only manages memory for you, but it forbids you from trying to do it yourself. It's illegal to manually send retain/release/auto release when using ARC.
Is ARC available in Xcode?
"ARC is available in Xcode 4.2, currently in beta, and only when compiling with Clang (a.k.a. "Apple LLVM compiler"). The setting is called, obviously enough, "Objective-C Automatic Reference Counting". Turn it on, and off you go.
How to convert Xcode to ARC?
Xcode 4.2 or later provides a way to convert code to ARC. As of Xcode 4.5, it is found by choosing Edit > Refactor > Convert to Objective-C ARC... Although Xcode will automatically convert most code, some code may have to be converted manually. Xcode will inform the developer when more complex use cases arise, such as when a variable is declared inside an autorelease pool and used outside it or when two objects need to be toll-free bridged with special casts.
What is ARC in Clang?
Automatic Reference Counting ( ARC) is a memory management feature of the Clang compiler providing automatic reference counting for the Objective-C and Swift programming languages. At compile time, it inserts into the object code messages retain and release which increase and decrease the reference count at run time, marking for deallocation those objects when the number of references to them reaches zero.
What is a weak reference in ARC?
Zeroing weak references is a feature in Objective-C ARC that automatically clears (sets to nil) weak-reference local variables, instance variables, and declared properties immediately before the object being pointed to starts deallocating. This ensures that the pointer goes to either a valid object or nil, and avoids dangling pointers. Prior to the introduction of this feature, "weak references" referred to references that were not retaining, but were not set to nil when the object they pointed to was deallocated (equivalent to unsafe_unretained in ARC), thus possibly leading to a dangling pointer. The programmer typically had to ensure that all possible weak references to an object were set to nil manually when it was being deallocated. Zeroing weak references obviates the need to do this.
Why is zeroing weak reference only available on Mac?
Zeroing weak references are only available in Mac OS X Lion (10.7) or later and iOS 5 or later, because they require additional support from the Objective-C runtime. However, some OS X classes do not currently support weak references. Code that uses ARC but needs to support versions of the OS older than those above cannot use zeroing weak references, and therefore must use unsafe_unretained weak references. There exists a third-party library called PLWeakCompatibility [1] that allows one to use zeroing weak references even on these older OS versions.
How does Swift differ from Objective C?
Swift also differs from Objective-C in its usage and encouragement of value types instead of reference types. Most types in the Swift standard library are value types and they are copied by value, whereas classes and closures are reference types and passed by reference. Because value types are copied when passed around, they are deallocated automatically with the reference that created them.
How does ARC differ from tracing garbage collection?
ARC differs from tracing garbage collection in that there is no background process that deallocates the objects asynchronously at runtime. Unlike tracing garbage collection, ARC does not handle reference cycles automatically. This means that as long as there are "strong" references to an object, it will not be deallocated.
Does Apple use ARCLite?
Apple Inc. deploys ARC in their operating systems, such as macOS ( OS X) and iOS. Limited support (ARCLite) has been available since Mac OS X Snow Leopard and iOS 4, with complete support following in Mac OS X Lion and iOS 5. Garbage collection was declared deprecated in OS X Mountain Lion, in favor of ARC, and removed from the Objective-C runtime library in macOS Sierra.
What is ARC in Swift?
As a modern, high-level programming language, Swift handles much of the memory management of your apps and allocates or deallocates memory on your behalf. It does so using a feature of the Clang compiler called Automatic Reference Counting, or ARC. In this tutorial, you’ll learn all about ARC and memory management in Swift.
Why does Swift use ARC?
Swift uses ARC to be predictable and efficient in resource-constrained environments. ARC works automatically, so you don’t need to participate in reference counting, but you do need to consider relationships between objects to avoid memory leaks.
Does ARC count reference?
ARC works automatically, so you don’t need to participate in reference counting, but you do need to consider relationships between objects to avoid memory leaks. This is an important requirement that is often overlooked by new developers.
Can an object deallocate a reference count?
Since each has a non-zero reference count, neither object can deallocate. This is a strong reference cycle. It fools ARC and prevents it from cleaning up. As you can see, the reference count at the end is not zero, and even though neither is still required, object1 and object2 are never deallocated.
What does ARC do?
All that ARC does is insert retains and releases into your code when it compiles it, exactly where you would have — or at least should have — put them yourself. That makes ARC just as fast as manually managed code, and sometimes even a bit faster because it can perform certain optimizations under the hood.
Why is there no owner for a string in Xcode?
There is no owner for the string object (because str is weak ) and the object will be deallocated immediately after it is created . Xcode will give a warning when you do this because it’s probably not what you intended to happen (“Warning: assigning retained object to weak variable; object will be released after assignment”).
What does automatic reference count mean?
With Automatic Reference Counting enabled, the compiler will automatically insert retain, release and autorelease in the correct places in your program. You no longer have to worry about any of this, because the compiler does it for you. I call that freaking awesome. In fact, using ARC is so simple that you can stop reading this tutorial now. ;-)
What is static analyzer Xcode?
The static analyzer from Xcode is a great help in finding these kinds of problems but ARC goes a step further. It avoids memory management problems completely by automatically inserting the proper retains and releases for you!
What are the rules of ARC?
The new rules you have to learn for ARC are quite simple. With manual memory management you needed to retain an object to keep it alive. That is no longer necessary, all you have to do is make a pointer to the object. As long as there is a variable pointing to an object, that object stays in memory. When the pointer gets a new value or ceases to exist, the associated object is released. This is true for all variables: instance variables, synthesized properties, and even local variables.
Does ARC work on Objective C?
Automatic Reference Counting also has a few limitations. For starters, ARC only works on Objective-C objects. If your app uses Core Foundation or malloc () and free (), then you’re still responsible for doing the memory management there. We’ll see examples of this later in the tutorial. In addition, certain language rules have been made stricter in order to make sure ARC can always do its job properly. These are only small sacrifices, you gain a lot more than you give up!
Is ARC a runtime feature?
It is important to realize that ARC is a feature of the Objective-C compiler and therefore all the ARC stuff happens when you build your app. ARC is not a runtime feature (except for one small part, the weak pointer system), nor is it *garbage collection* that you may know from other languages.
