Return multiple objects from a method in Objective-C

The typical ways to pass back multiple values are to:

• Add extra parameters by reference (ex. typically NSErrors are passed this way)
• Pass them back in some other struct or object, typically an NSDictionary or a custom class

The above are good solutions for many situations, but here is another solution that may work best in other situations:

Add a block to your method:

- (void)myMethodWithMultipleReturnObjectsForObject:(id)object returnBlock:(void (^)(id returnObject1, id returnObject2))returnBlock
{
    // do stuff

    returnBlock(returnObject1, returnObject2);
}

Then use the method like this:

[myMethodWithMultipleReturnObjectsForObject:object returnBlock:^(id returnObject1, id returnObject2) {
    // Use the return objects inside the block
}];

The return objects in the above example are only usable within the block, so if you want to keep them around for use outside the block, just set some __block vars.

// Keep the objects around for use outside of the block
__block id object1;
__block id object2;
[myMethodWithMultipleReturnObjectsForObject:object returnBlock:^(id returnObject1, id returnObject2) {
    object1 = returnObject1;
    object2 = returnObject2;
}];

Another way you can do it is have the user pass a pointer which they want to use to hold the data. Here is a sample that returns an array and uses pointers to give you an int value and another array. EDIT ok here is the working version I just tested it myself:

- (NSMutableArray*)doStuff:(int*)container returnedArray:(NSMutableArray*)arrayContainer{
   int a = 4;
   *container = a;
   [arrayContainer removeAllObjects];
   [arrayContainer addObject:@"object"];
   return [NSMutableArray arrayWithObjects:@"object",nil];
}

That way you could say like:

int value = 0;
NSMutableArray* new = [NSMutableArray array];
[self doStuff:&value returnedArray:new];

And it basicly works like a return!

You might want to consider returning a struct.

typedef struct {
    NSMutableArray *array1;
    NSArray *array2;
    NSInteger integer;
} MyAwesomeReturnValue;

Your method could now look like this:

- (MyAwesomeReturnValue)myAwesomeMethod:(NSMutableArray *)parameter
{
    MyAwesomeReturnValue retval;
    retval.array1 = parameter;
    retval.array2 = [NSArray array];
    retval.integer = 5;

    return retval;
}

And you'd use it like:

- (void)anotherAwesomeMethod
{
    NSMutableArray *array = [NSMutableArray array];
    MyAwesomeReturnValue returnedValue = [self myAwesomeMethod:array];

    NSLog(@"%@", returnedValue.array1);
    NSLog(@"%@", returnedValue.array2);
    NSLog(@"%d", returnedValue.integer);
}

Hope that helped. ;)