In theory, you are right. But in practice, chance of collision in many
real-world scenarios is 100%. As an example, consider the following
scenario:
I have a .blend with some objects ("A"), all objects in it already have
generated UUID. I open the file, edit something, save as different file
("B"). Then again I open the original file, and save it under different
name ("C"). Then I create new empty file and append objects from "B" and
"C". If I append the same object from both files, there will be UUID
collision. But this is not an issue as long as there is a check to make
sure that each appended or duplicated object has unique UUID in the
scope of the current .blend file, and if not, just reset its UUID (it
can be generated later on demand if necessary). I think this is
preferable to blindly regenerating (or dropping) UUIDs, since if there
is no collisions, I may have a reason to preserve UUIDs as is when
appending my objects. Besides, Blender already does collision detection
for object names to automatically rename them if it happens. But for
UUID, it is safe to just invalidate it if it conflicts with another UUID
of already existing data block, and generate a new one later when necessary.
On 21/11/20 6:33 pm, Harley Acheson via Bf-committers wrote:
It would be impossible task to make them truly unique across all .blend
files, there are always a possibility of collision.
UUIDs have limitations...will not change unless there is a collision).
That does not sound right.
If 128-bit UUID are implemented properly according to standard, the chances
of collision is *zero* *for all practical purposes*. The chances of
collision are so low that implementations can ignore it. To get to a 50%
probability of at least one collision you need to create 2.71 quintillion -
so generating a billion of them per second for 85 years. Just to get a
one-in-a-billion chance of a duplicate requires making 103 trillion.
Cheers, Harley
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