Re: On NSIncrementalStore UUID Uniqueness
Re: On NSIncrementalStore UUID Uniqueness
- Subject: Re: On NSIncrementalStore UUID Uniqueness
- From: Daryle Walker <email@hidden>
- Date: Thu, 19 Jan 2017 16:18:42 -0500
> On Jan 16, 2017, at 12:08 PM, Charles Srstka <email@hidden> wrote:
>
>> On Jan 14, 2017, at 4:41 AM, Daryle Walker <email@hidden <mailto:email@hidden>> wrote:
>>
>> Could I base the UUID off a hash of the URL? Maybe, but it wouldn’t survive file moves. There are file references in macOS, which would be more stable, but I read that there’s a bug in the URL class where it would degrade file-reference URLs to standard-file URLs, so that’ll be problematic. Another solution would to create bookmark data from a file URL and take a hash of that. But are multiple bookmark data blocks of the same file URL consistent enough for this idea to work?
>
> The thing with file reference URLs degrading to file path URLs is in the Swift is actually not a bug, it’s deliberate (https://bugs.swift.org/browse/SR-2728 <https://bugs.swift.org/browse/SR-2728>). The Swift team decided that file reference URLs are not appropriate for the Swift URL value type. However, if you’re using Objective-C, file reference URLs will still work fine, and you can always make an Objective-C wrapper that stores a file reference URL and use that from Swift.
I looked at some code that gives a workaround for the file-reference URL problem. It grabs the reference ID as a 128-bit value, dumps it into 2 64-bit values, then sprinkles those onto a URL string template. Since UUIDs are 128-bit values, I could just copy a reference ID directly into a UUID. However it means existing files would have a different style, possibly overlapping, than new files (which would take a random UUID). Maybe it’ll be better to always use a random UUID, the implementers do in practice.
—
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT mac DOT com
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