> On Mar 30, 2015, at 7:59 PM, Kevin Perry <kpe...@apple.com> wrote:
> 
> -replaceItemAtURL:… relies on the atomicity of the POSIX rename() function in 
> order to safely do its operation. Since rename() doesn’t work across volumes 
> (returning EXDEV), the two URLs must be on the same volume.
> 
> If you’re using a temporary directory with replaceItemAtURL:…, you want to 
> use -[NSFileManager URLForDirectory:inDomain:appropriateForURL:create:error:] 
> with NSItemReplacementDirectory, passing it the to-be-replaced item URL. This 
> will get you an appropriate temporary directory on the target volume to 
> ensure -replaceItemAtURL:… won’t fail due to rename's EXDEV.
> 
>> On Mar 30, 2015, at 4:44 PM, Daryle Walker <dary...@mac.com 
>> <mailto:dary...@mac.com>> wrote:
>> 
>> NSFileManager’s “- moveItemAtURL: toURL: error:” method does a copy if the 
>> source and destination file-URLs are on different volumes. Does “- 
>> replaceItemAtURL: withItemAtURL: backupItemName: options: resultingItemURL: 
>> error:” do similar? The docs for the latter don’t mention it. I’m worried 
>> since those docs do mention temporary directories, that we have to do 
>> different-volume detection (possibly harder than in the pre-X days) and 
>> copying manually. I don’t want to do that, since Apple already includes that 
>> logic in the former method.

So I have to: (1) call URLForDirectory… to make sure there’s an appropriate 
temporary directory, (2) call moveItemAtURL… to relocate the downloaded file 
from the volume NSURLSession used to the one made in the first step, and (3) 
call replaceItemAtURL… for the final move, right? Is there a way to easily 
determine if two file objects are in the same volume, to skip the second step 
if unneeded? (Or is there a way to tell NSURLSession which volume to put its 
temporary files in advance?…)

— 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com 

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