Re: [iPhone] How to create a unique string
Re: [iPhone] How to create a unique string
- Subject: Re: [iPhone] How to create a unique string
- From: Douglas Davidson <email@hidden>
- Date: Thu, 13 May 2010 08:59:26 -0700
On May 13, 2010, at 8:52 AM, Louis Gerbarg wrote:
>>> No it's not, as can easily be proven by observing that there are only a finite number of 40 character strings. A UUID is probabilistically unique.
>>
>> CFUUID includes the MAC address, so unless your MAC address is cloned
>> or you manage to generate two UUIDs on the same device in the same
>> 100ns time interval or the calendar rolls over (which will take about
>> 3700 years), they are entirely unique within the universe of CFUUID
>> strings.
>
> No, it doesn't use the MAC address. MAC addresses are uses as part of type 1 uuids, CFUUID has generated type 4 (random) uuids by default since Tiger, and has always generated type 4 on iPhone. If you look at the source to CF there is a way to force it to generate type 1 uuids, but I doubt that is supported.
The use of the MAC address was removed because of privacy concerns. CFUUID generation is only probabilistically unique, but the probability of collisions is vanishingly small.
Douglas Davidson
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