When trying to use -retain, -release, and -dealloc while building my application using automatic reference counting in Xcode 4.2, I get an error like the following:
Automatic Reference Counting forbids
explicit message send of 'dealloc'
Why am I seeing this error? Are -retain, -release, and -dealloc no longer allowed under automatic reference counting?
Basically:
When using ARC, it's all or nothing. Either the compiler is managing all of the retains/releases/deallocs for you, or it is doing nothing. You cannot intersperse your own calls to them, because the compiler wants to do it all itself. It can make absurd optimizations by doing this (for example, a method that returned an autoreleased object under Manual Memory Management may now produce an object that never ends up in an autorelease pool). If you were to start sprinkling in your own calls to retain and release, then the compiler would have to work with these and wouldn't be able to perform a lot of the optimizations that it wants (and that you should want).
And as an added bonus, invoking -retainCount is now a compiler error! OH HAPPY DAY!
in response to AliSoftware: we CNA mix ARTC and not-ARC frameworks, and also arc and not-ARC source.
(I did it..)
The basic ideas are:
1) compiler will insert/remove calls as a very-very-good cocoa programmer can do
2) cocoa is ANYWAY C code, so we have separate compilations, so the linker CAN link binaries produced by multiple sources. Think it as we can mix asm and cocoa, or C and pascal...
in main opinion the Appleadvantege over c# / java is here: we are alway allows to mix, and, using a COMPILER technique 8non a runtime..) we can rush performance beyond.
Under automatic reference counting, retain, release, and dealloc are not allowed.
If you have an existing code, you can keep using it as is with the -fno-objc-arc you can selectively disable ARC on any file.
If you want to disable ARC on MULTIPLE files:
Select desired files at Target/Build Phases/Compile Sources in Xcode
PRESS ENTER. (double click selects only one file)
Type -fno-objc-arc
Press Enter or Done
As I have pointed out in my answer on Xcode ARC, you can compile specific source files as non-ARC. Dave DeLong's answer is a bit off. It doesn't include the fact that you can instruct the compiler to compile source as non-ARC in an ARC-enabled project (as explained here).
Related
Hello I am completely new to Apple development
I used this code in my project
https://github.com/vladinecko/accordion-uitableview/tree/master/AccordionTableView
, project releases the memory itself using autorelease
What made me disable the ARC
Because ARC does not allow the use of autorelease
My question is whether to delete the autorelease from the code
And use ARC or i can not do it and I need to have to release the memory for myself
You could leave the code as-is—you can compile some files using ARC and others not, but that’s going to be messy and hard to maintain.
What I’d recommend doing is running Xcode’s ARC-ifying on the code, to get rid of retain and release and autorelease.
In Xcode 5, look under the “Edit” menu for “Refactor”, and select “Convert to ObjC ARC”.
Apparently AccordionTableView does not use ARC, whereas in your project you are using it.
So you have three options
Switch off ARC only for the separate compilation units, which are from AccordionTableView
Adapt the code snippet from AccordionTableView project with ARC guidelines
Switch your own project to not use ARC
First, being new to Objective-C development you need to learn how memory management works. Google for "Apple memory management" and you should find relevant documents.
Before ARC, people did memory management by hand. With ARC, ARC does it for you. The exact same memory management operations should happen, except that with ARC you have less programmer work, and chances to get it right are better.
You have two choices: Either turn ARC off for individual files. This is done in Xcode / target settings / Build phases / Compile sources by adding -fno-objc-arc to the build settings for individual files where you don't want to use ARC. If you use the same files in different projects, you have to do this in every target.
The other choice is to convert the files to ARC. Let the compiler run, remove offending memory management code, which is mostly retain / release / autorelease. If the code uses CoreFoundation functions, then you really need to understand memory management, just hope it doesn't. Use "Analyze" to let the compiler check very carefully that everything is fine.
I am trying to convert an old code to an ARC code.
However, i am getting a build error at the following line
[[token retain] autorelease];
I get 3 errors in the following order:
-'autorelease' is unavailable: not available in automatic reference counting mode
-[rewriter] it is not safe to remove an unused 'autorelease' message; its receiver may be destroyed immediately
-ARC forbids explicit message send of 'autorelease'
If i remove this particular line, then the code compiles correctly
If that is all that is on the line, you can probably just remove it. That code claims a reference to the object but also says you don't want to worry about releasing later, but with ARC you don't have to worry about it.
I am guessing that Xcode did not get rid of it automatically because of lack of context. If it had been in a more common location, such as in a return statement, it would be obvious what the intent was. When it is all by itself, it could be, but probably is not, something more complicated.
ARC manages your memory for you, so you don't need to call "autorelease", "release", "retain" etc. With ARC the compiler retain and release objects as necessary for you so you don't have to explicitly make these calls. If you want to manually manage your memory disable ARC, or you can use the compiler flag "-fno-objc-arc" to disable ARC on a specific class.
ARC means you don't have to use release, retain or those other pesky memory management things. ARC add them all for you automatically when you compile the app. Read more here
If you have old code where it would not be the best solution to remove all the memory management calls, then check this answer to disable ARC for particular files
This might be a silly question, but I just wanted to know. I want my code to detect if ARC is enabled, programmatically. How do I do that? Is there is any flag that I could check? Actually the problem is that, I have written an open-source library. I have used release and retain in it. if some one else uses my library files using ARC enabled, I dont want them to get any errors. how do I achieve this? or is there any possible ways I can provide any tools to compile my library before using it?
#if !__has_feature(objc_arc)
//Do manual memory management...
#else
//Usually do nothing...
#endif
This is of course a compile-time check, you cannot check for ARC at runtime.
An alternative would be to set the -fno-objc-arc compiler flag for your files that use manual memory management in a project that otherwise uses ARC.
Whether you want to bother with this at all or just use ARC everywhere depends on how backward-compatible you want/need to be. Code that supports both ARC and MRC can get quite hard to read and maintain.
You don't detect it programmatically, it operates based on translations. That is, it is not like Garbage Collection -- which is process-wide, required all linked libraries to support (and implement it correctly in that mode). You can have some files compiled with ARC, and some without.
However, you can detect it at compilation.
As far as the distribution of your library: I would not bother with a translation based system, where ref count ops are conditionally enabled. I would (personally) just support one model (MRC in your case, until you choose to migrate it to ARC), then expect people to link to the library, or if they compile it in a target they configure, to disable ARC. Conditionally enabling/disabling code based on the presence of a feature is asking for tough bugs, particularly when it's likely to affect 9% of your library's lines of code.
NO, you can't, Xcode would not compile in ARC projects if your source uses retain-release
I just downloaded an Xcode project, and I get all these errors about "ARC Restrictions." What are these, and how can I remove them?
There are basically two versions of memory management in objective-c. ARC and... well, "Not ARC" :-) You probably downloaded a project, which doesn't use ARC already. Simplest way of resolving your problem is to instruct the compiler to treat your sources as "Not ARC". Explained here.
And here is a good tutorial that should get you started with ARC.
ARC automatically keep track of memory release and retain so you can not release and retain any memory manually.
ARC also doesn't allow any method to be get called at compile time which prototype is not declared in interfaces.
It has also introduced new #autoreleasepool block. so it doesn't not allow older autorelease of an object automatically
However it has allowed dealloc method to be written, but it doesn't allowed [super dealloc] to be get called.
There are much more written about ARC at this blog you can checkt it here
You can covert your project to ARC using xcode in following way.
Go to Edit -> Refactor -> Convert to objective c arc.
However it has some compatibility issue with git repository so it does not convert when .git folders are there in projects. so you will have to remove it first and then convert it. check this link
I'm trying to compile using the LLVM GCC 4.0 compiler, and I get this error in multiple of my .m files: ARC forbids explicit message send of 'release'
I've tried using -fno-objc-arc as a compiler flag but that returns the error: Unrecognized command line option "-fno-objc-arc".
How can I solve this?
Simply remove all calls to -release. You're not allowed to call -release under ARC because the compiler will insert all the necessary retain/release calls for you. Read more about ARC here.
The other way is to use the conversion tool, and Xcode can convert your project to ARC (including removing these calls) for you:
To disable ARC entirely, change your build settings:
However I'd recommend you start using ARC, it will make things a lot easier and actually faster too.
If you happen to be using the ASI (http://allseeing-i.com/ASIHTTPRequest/How-to-use) api, refer to this answer as it needs to be built using -fno-obj-arc flags for specific classes... Files doesn't support the ARC feature, how to deal with and refer to the answer titled 'Disable ARC for that one class'