Question

From a related thread, how should I have known the “mailString” below was already autoreleased?

//
+ (void) sendEmail:(NSString *) subject withBody:(NSString *)body {
 NSString *mailString = [NSString stringWithFormat:@"mailto:?@&subject=%@&body=%@",
       [subject stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding],
       [body  stringByAddingPercentEscapesUsingEncoding:NSASCIIStringEncoding]];
 [[UIApplication sharedApplication] openURL:[NSURL URLWithString:mailString]];
 [mailString autorelease];
 }

Answer 1

stringWithFormat: is a convenience function that returns an autoreleased object.

I cannot recomment the Memory Management Guide highly enough. It really is worth reading, probably more than once.