Make a unique filesystem path, without creating the file

Jon Ribbens jon+usenet at unequivocal.co.uk
Mon Feb 22 19:08:48 EST 2016


On 2016-02-22, Steven D'Aprano <steve at pearwood.info> wrote:
> On Tue, 23 Feb 2016 05:48 am, Marko Rauhamaa wrote:
>> Jon Ribbens <jon+usenet at unequivocal.co.uk>:
>>> I was under the impression that the point of UUIDs is that you can be
>>> *so* confident that there won't be a collision that for all practical
>>> purposes it's indistinguishable from being certain.
>> 
>> Yes, if you generate a random 128-bit number, it will be unique --
>
> If you generate a second random 128 bit number, you have a chance of 1 in
> 2**128 of a collision. All you can say is that it will be *very probably*
> unique. (I might even allow "almost certainly" unique.)

If you are not prepared to say that something with a
340282366920938463463374607431768211455 /
340282366920938463463374607431768211456 chance of being true
is not "certainly true" then I'm not sure how you would not
be too scared to ever leave the house. Or not leave the house.
I mean, you're probably going to be hit by 10^25 meteorites,
which sounds painful.

> If you generate 2**128 + 1 such numbers, you are *guaranteed* to

... have expired due to the heat death of the universe.


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