如何理解保留计数

Question

I used following link for understand the retain count.
retain count in iphone
As per that question output is :

NSString *str = [[NSString alloc] initWithFormat:@"a,b,c,d"];
NSArray  *anArray =[[NSArray alloc]init];
NSLog(@"Retain count: %i", [anArray retainCount]);
anArray=[str componentsSeparatedByString:@","];
NSLog(@"Retain count: %i", [anArray retainCount]);  

OUTPUT

Retain count: 2
Retain count: 1

When I tried this code in my example :

NSString *str = [[NSString alloc] initWithFormat:@"a,b,c,d"];
NSArray  *anArray=[[NSArray alloc]init];
NSLog(@"Retain count: %i", [anArray retainCount]);
anArray=[str componentsSeparatedByString:@","];
NSLog(@"Retain count: %i", [anArray retainCount]);

Then OUTPUT is

Retain count: 51
Retain count: 1

I can't understand why the retain count of NSArray is 51 and after assigning value in array it becomes 1.

I also read
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/MemoryMgmt/Articles/MemoryMgmt.html
http://ranga-iphone-developer.blogspot.in/2011/11/what-is-retain-count-or-reference.html
iOS about retainCount
and other tutorial. but I can't understand the value of Retain count: 51 .

Pleas Help me.
Thank You.

Answer 1

See WhenToUseRetainCount.com for an explanation on when and why to use retainCount .

The count is 51 due to an implementation detail of empty arrays. It goes to 1 because you are getting the count of a different object.

If using manual-retain-release, then this pattern is a leak:

Foo *foo = [[Foo alloc] init];
foo = [someObject retrieveTheFooness];

The allocated object is leaked.

Use ARC.