Difference between [[NSDate date] retain] and [[NSDate alloc] init]

Question

As both of the following serves the same purpose,

today = [[NSDate date] retain];    

and

today = [[NSDate alloc] init]; 
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Answer 1

When you do this:

[NSDate date];

…a new NSDate is created which will automatically be released (not deallocated!) at the end of the event loop. You can, of course, retain it to keep it around longer.

When you do this:

[[NSDate alloc] init];

…a new NSDate is created which you should release when you’re done with it.

From a memory management standpoint, the main differece between [[NSDate date] retain] and the alternative is that this NSDate will be around at least until the end of the event loop. If you’re just creating a few objects, it doesn’t matter. But, if you create (and release) a lot of objects — say, while processing data in a loop — using the former pattern could cause the memory usage of your application to spike (and then drop suddenly at the end of the event loop). With the latter pattern, the object gets destroyed as soon as you release it.