Objective C - Assign Copy Retain

Question

I m new to Objective C  I have basic knowledge in C  including the concept of pointers  I have two basic questions    Can someone explain the difference between assign copy  and retain with some analogy  How do you handle a function which returns pointer variable  and how do you perform messaging through a return pointer

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The Memory Management Programming Guide from the iOS Reference Library has basics of assign, copy, and retain with analogies and examples.

copy Makes a copy of an object, and returns it with retain count of 1. If you copy an object, you own the copy. This applies to any method that contains the word copy where “copy” refers to the object being returned.

retain Increases the retain count of an object by 1. Takes ownership of an object.

release Decreases the retain count of an object by 1. Relinquishes ownership of an object.

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Updated Answer for Changed Documentation  The information is now spread across several guides in the documentation  Here s a list of required reading    Cocoa Core Competencies  Declared property Programming with Objective-C  Encapsulating Data Transitioning to ARC Release Notes Advanced Memory Management Programming Guide Objective-C Runtime Programming Guide  Declared Properties   The answer to this question now depends entirely on whether you re using an ARC-managed application  the modern default for new projects  or forcing manual memory management   Assign vs  Weak - Use assign to set a property s pointer to the address of the object without retaining it or otherwise curating it  use weak to have the property point to nil automatically if the object assigned to it is deallocated  In most cases you ll want to use weak so you re not trying to access a deallocated object  illegal access of a memory address -  EXC BAD ACCESS   if you don t perform proper cleanup   Retain vs  Copy - Declared properties use retain by default  so you can simply omit it altogether  and will manage the object s reference count automatically whether another object is assigned to the property or it s set to nil  Use copy to automatically send the newly-assigned object a -copy message  which will create a copy of the passed object and assign that copy to the property instead - useful  even required  in some situations where the assigned object might be modified after being set as a property of some other object  which would mean that modification mutation would apply to the property as well

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NSMutableArray  array     NSMutableArray alloc  initWithObjects   First    Second   nil   NSMutableArray  copiedArray    array mutableCopy   NSMutableArray  retainedArray    array retain     retainedArray addObject   Retained Third     copiedArray addObject   Copied Third     NSLog   array       array   NSLog   Retained Array       retainedArray   NSLog   Copied Array       copiedArray    array         First      Second       Retained Third    Retained Array         First      Second       Retained Third    Copied Array         First      Second       Copied Third

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assign   assign is a default property attribute  assign is a property attribute tells the compiler how to synthesize the property   s setter implementation  copy    copy is required when the object is mutable copy returns an object which you must explicitly release  e g   in dealloc  in non-garbage collected environments you need to release the object when finished with it because you are retaining the copy  retain    specifies the new value should be sent    -retain    on assignment and the old value sent    -release    if you write retain it will auto work like strong Methods like    alloc    include an implicit    retain

[ios] Objective C - Assign, Copy, Retain

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