Mutable collection worst case

gistfile1.txt

//here is an array factory method

@interface Foo: NSObject

@end

@implementation Foo

+ (NSArray *)newArray
{
    NSMutableArray *array = [NSMutableArray array]
    [array addObject:@"Hello"];
    [array addObject:@"World"];
    return array; //don't both copying, to improve peformance
}

@end

//here is a class that accepts an array, and uses copy semantics (according to best practice)

@interface Bar: NSObject

@property (nonatomic, copy) NSArray *array;

@end

@implementation Bar

@end

//here is where I use it

NSArray *foo = [Foo newArray];
NSMutableArray *bars = [NSMutableArray array];
for (int i = 0; i < 10000; i++) {
    BarClass *bar = [Bar new];
    bar.array = foo;
    [bars addObject:bar];
}

//problem: I'm assuming this will be efficient because I'm adding the same instance of foo to each new Bar.
//but unfortunately, because foo is secretly mutable, I'm actually copying it each time around the loop
//if +newArray had returned an immutable array by copying internally, I'd avoid 9999 additional copies