Return a NSMutableArray?

samurle · February 2012

I'm trying to return a NSMutableArray from a method.
I prefer not to use autorelease.

Is this a valid allocation and release, or will it leak?
Will the alloc go out of scope as soon as the getArray method ends?


-(NSMutableArray *)getArray {

 NSMutableArray *arr = [[NSMutableArray alloc] init];

 [arr addObject:@\"Test1\"];
 [arr addObject:@\"Test2\"];
 [arr addObject:@\"Test3\"];

 return arr;
}

-(void) myMethod {

 NSMutableArray *arr = [self getArray];

 for(NSString *str in arr) {
    NSLog(@\"string: %@\", str );
 }

 [arr release];
}

BrianSlick · February 2012

It doesn't leak as you have it, but you aren't following convention. Just return an autoreleased array.

Duncan C · February 2012

samurle;406461 said:
I'm trying to return a NSMutableArray from a method.
I prefer not to use autorelease.

Is this a valid allocation and release, or will it leak?
Will the alloc go out of scope as soon as the getArray method ends?
-(NSMutableArray *)getArray {

 NSMutableArray *arr = [[NSMutableArray alloc] init];

 [arr addObject:@\"Test1\"];
 [arr addObject:@\"Test2\"];
 [arr addObject:@\"Test3\"];

 return arr;
}

-(void) myMethod {

 NSMutableArray *arr = [self getArray];

 for(NSString *str in arr) {
    NSLog(@\"string: %@\", str );
 }

 [arr release];
}

There is a strong convention in Cocoa programming that methods like this should return an autoreleased object, and the caller should retain it if they want to keep it.

If you want to return a retained object, have the name begin with "new".

In fact, the LLVM compiler uses this naming convention when it does code analysis. It expects methods to return autoreleased objects unless their names begins with new, alloc, copy, or mutableCopy. Methods who's names DO start with new, alloc, copy, or mutableCopy are expected to return retained object.

This is a really, really good idea to follow. When you follow that rule, it's obvious what you need to do with any given object.

samurle · February 2012

Duncan C;406584 said:
There is a strong convention in Cocoa programming that methods like this should return an autoreleased object, and the caller should retain it if they want to keep it.

If you want to return a retained object, have the name begin with "new".

In fact, the LLVM compiler uses this naming convention when it does code analysis. It expects methods to return autoreleased objects unless their names begins with new, alloc, copy, or mutableCopy. Methods who's names DO start with new, alloc, copy, or mutableCopy are expected to return retained object.

This is a really, really good idea to follow. When you follow that rule, it's obvious what you need to do with any given object.

Thanks, that's exactly what I want to do. Return a retained object, but not an autorelease object.

Hopefully, returning a retained object does not automatically make it an autorelease object
behind the scenes?

I replaced:


getArray

with:


newArray

And the compiler warning message went away. I didn't know that was possible.

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