What should i dealloc

Applying these precise-lifetime semantics strictly would be prohibitive. Many useful optimizations that might theoretically decrease the lifetime of an object would be rendered impossible. Essentially, it promises too much. Nonetheless, it is sometimes useful to be able to force an object to be released at a precise time, even if that object does not appear to be used.

This is likely to be uncommon enough that the syntactic weight of explicitly requesting these semantics will not be burdensome, and may even make the code clearer. A program is ill-formed if it contains a method definition, message send, or selector expression for any of the following selectors:.

The others were banned after weighing three options for how to deal with message sends:. At best, such code would do twice as much work as necessary; quite frequently, however, ARC and the explicit code would both try to balance the same retain, leading to crashes.

Ignoring them would badly violate user expectations about their code. While it would make it easier to develop code simultaneously for ARC and non-ARC, there is very little reason to do so except for certain library developers. Banning them has the disadvantage of making it very awkward to migrate existing code to ARC. The best answer to that, given a number of other changes and restrictions in ARC, is to provide a specialized tool to assist users in that migration.

Implementing these methods was banned because they are too integral to the semantics of ARC; many tricks which worked tolerably under manual reference counting will misbehave if ARC performs an ephemeral extra retain or two.

If absolutely required, it is still possible to implement them in non-ARC code, for example in a category; the implementations must obey the semantics laid out elsewhere in this document.

A program is ill-formed if it contains a message send or selector expression for the selector dealloc. There are no legitimate reasons to call dealloc directly. A class may provide a method definition for an instance method named dealloc. This method will be called after the final release of the object but before it is deallocated or any of its instance variables are destroyed.

Even though ARC destroys instance variables automatically, there are still legitimate reasons to write a dealloc method, such as freeing non-retainable resources. Failing to call [super dealloc] in such a method is nearly always a bug. Sometimes, the object is simply trying to prevent itself from being destroyed, but dealloc is really far too late for the object to be raising such objections. Somewhat more legitimately, an object may have been pool-allocated and should not be deallocated with free ; for now, this can only be supported with a dealloc implementation outside of ARC.

The instance variables for an ARC-compiled class will be destroyed at some point after control enters the dealloc method for the root class of the class. The ordering of the destruction of instance variables is unspecified, both within a single class and between subclasses and superclasses.

The traditional, non-ARC pattern for destroying instance variables is to destroy them immediately before calling [super dealloc]. Unfortunately, message sends from the superclass are quite capable of reaching methods in the subclass, and those methods may well read or write to those instance variables. In most code, the difference is not observable. It can, however, be observed if an instance variable holds a strong reference to an object whose deallocation will trigger a side-effect which must be carefully ordered with respect to the destruction of the super class.

Such code violates the design principle that semantically important behavior should be explicit. A simple fix is to clear the instance variable manually during dealloc ; a more holistic solution is to move semantically important side-effects out of dealloc and into a separate teardown phase which can rely on working with well-formed objects.

To simplify the use of autorelease pools, and to bring them under the control of the compiler, a new kind of statement is available in Objective-C. It is written autoreleasepool followed by a compound-statement , i. Upon entry to this block, the current state of the autorelease pool is captured. When the block is exited normally, whether by fallthrough or directed control flow such as return or break , the autorelease pool is restored to the saved state, releasing all the objects in it.

When the block is exited with an exception, the pool is not drained. A program is ill-formed if it refers to the NSAutoreleasePool class. Autorelease pools are clearly important for the compiler to reason about, but it is far too much to expect the compiler to accurately reason about control dependencies between two calls. The introduction of a new scope is unfortunate but basically required for sane interaction with the rest of the language.

Not draining the pool during an unwind is apparently required by the Objective-C exceptions implementation. The self parameter variable of an Objective-C method is never actually retained by the implementation. It is undefined behavior, or at least dangerous, to cause an object to be deallocated during a message send to that object.

To make this safe, for Objective-C instance methods self is implicitly const unless the method is in the init family. Further, self is always implicitly const within a class method. This is an optimization made possible because fast enumeration loops promise to keep the objects retained during enumeration, and the collection itself cannot be synchronously modified.

The implicit const capture variables created when evaluating a block literal expression have the same ownership semantics as the local variables they capture. The capture is performed by reading from the captured variable and initializing the capture variable with that value; the capture variable is destroyed when the block literal is, i.

The optimizer may remove such copies when it sees that the result is used only as an argument to a call. The standard Cocoa convention is that exceptions signal programmer error and are not intended to be recovered from. Making code exceptions-safe by default would impose severe runtime and code size penalties on code that typically does not actually care about exceptions safety.

Therefore, ARC-generated code leaks by default on exceptions, which is just fine if the process is going to be immediately terminated anyway. Programs which do care about recovering from exceptions should enable the option. Of course, potentially massive leaks are about as likely to take down the process as this corruption is if the program does try to recover from exceptions. Rationale: not all memory and resources are managed with reference counts; it is common for objects to manage private resources in their own, private way.

Typically these resources are completely encapsulated within the object, but some classes offer their users direct access for efficiency. This attribute informs ARC that it must tread lightly. The extension rules are somewhat intentionally vague. The autorelease pool limit is there to permit a simple implementation to simply retain and autorelease the receiver. The other limit permits some amount of optimization. However, the implementation never need account for uses after a return from the code which calls the method returning an interior pointer.

Tying this to precise lifetime semantics is ideal, as for local variables this requires a very explicit annotation, which allows ARC to trust the user with good cheer. A type is a C retainable pointer type if it is a pointer to possibly qualified void or a pointer to a possibly qualifier struct or class type.

In fact, ARC does not even know how to distinguish these types from arbitrary C pointer types. The intent of this concept is to filter out some obviously non-object types while leaving a hook for later tightening if a means of exhaustively marking CF types is made available. The pragma is accepted in all language modes. A program is ill-formed if it attempts to change files, whether by including a file or ending the current file, within the extent of this pragma.

These features are designed to make it relatively easy for API authors to quickly review and annotate their interfaces, in turn improving the fidelity of tools such as the static analyzer and ARC. The other qualifiers may be used on explicitly under-aligned memory. The runtime must provide a number of new entrypoints which the compiler may emit, which are described in the remainder of this section. Several of these functions are semantically equivalent to a message send; we emit calls to C functions instead because:.

We use the fused operations primarily as a code-size optimization, although in some cases there is also a real potential for avoiding redundant operations in the runtime.

Precondition: value is null or a pointer to a valid object. If value is null, this call has no effect. Otherwise, it adds the object to the innermost autorelease pool exactly as if the object had been sent the autorelease message.

Releases all the objects added to the given autorelease pool and any autorelease pools it encloses, then sets the current autorelease pool to the pool directly enclosing pool. While the interface is described as an explicit hierarchy of pools, the rules allow the implementation to just keep a stack of objects, using the stack depth as the opaque pool handle.

If this is not possible, the object is autoreleased as above. Equivalent to the following code:. The current value of object is left unspecified; otherwise, equivalent to the following code:.

If value is a null pointer or the object to which it points has begun deallocation, object is zero-initialized. Returns the value of object after the call. Otherwise returns null. Loading weak references would be inherently prone to race conditions without the retain. Otherwise, it performs a release operation exactly as if the object had been sent the release message. Otherwise, it performs a retain operation exactly as if the object had been sent the retain message.

Otherwise, it performs a retain operation followed by an autorelease operation. Precondition: value is null or a pointer to a valid block object. Otherwise, if the block pointed to by value is still on the stack, it is copied to the heap and the address of the copy is returned. Otherwise a retain operation is performed on the block exactly as if it had been sent the retain message. A method may be invoked by providing an object called the receiver and a list of formal arguments interspersed with the selector, like so: [ receiver foo : fooArg bar : barArg baz : bazArg ].

If a change increases the expressiveness of the language, for example by lifting a restriction or by adding new syntax, the change will be annotated with a revision marker, like so: ARC applies to Objective-C pointer types, block pointer types, and [beginning Apple 8.

Rationale We are not at liberty to require all code to be recompiled with ARC; therefore, ARC must interoperate with Objective-C code which manages retains and releases manually. Again, the storage for those variables is about to be deallocated. There's no sense assigning a new value just before that happens. As with instance variables, all strong references held in local variables will be released by the time they go out of scope. Search by keywords or tags Submit Search Clear search query Additional information about Search by keywords or tags Supported Searches:.

Overriding Dealloc with ARC. It's pointless setting foo and bar to nil in dealloc since after [super dealloc] the object they are in is gone. Yes, release all the properties of the object that are still retained. It will then send these three messages: [arr release]; [str release]; [mutableArr release]; To each of the three objects.

Thank you for your reply. I would like to ask about the 'when'. If i have 3 objects have to release. Then one of the objects becomes 0. Will the method be called? When you have 3 instances of the object in your code, and you do an [object1 release] on let's say the first object, you still have 2 instances left elsewhere, so it isn't called yet.

You'll need to release all instances of the object in order for dealloc to be called. Mark: Are you asking for "3 references to one object" or "3 distinct objects"? Georg Fritzsche, please see the post, I have updated it. Bob Gilmore Chuck Chuck k 29 29 gold badges silver badges bronze badges. Zaldy Zaldy 8 8 silver badges 16 16 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Thilo Thilo k 94 94 gold badges silver badges bronze badges.

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