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This file is part of Logtalk https://logtalk.org/ SPDX-FileCopyrightText: 1998-2026 Paulo Moura <pmoura@logtalk.org> SPDX-License-Identifier: Apache-2.0
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
uuid
This library implements a Universally Unique Identifier (UUID) generator. Currently version 1, version 4, and version 7 UUIDs are supported. For reference material, see e.g.
https://en.wikipedia.org/wiki/Universally_unique_identifier
Some backends provide time stamps with low granularity (e.g., seconds but not milliseconds or nanoseconds). To compensate, the generation of version 1 UUIDs uses 14 random bits for the clock sequence.
The generation of version 4 and version 7 UUIDs uses the `/dev/urandom` random number generator when available. This includes macOS, Linux, *BSD, and other POSIX operating-systems. On Windows, a pseudo-random generator is used, but randomized using the current wall time.
Version 7 UUIDs are time-ordered using a Unix Epoch timestamp in milliseconds, as specified in RFC 9562. They are recommended over version 1 UUIDs for new applications due to improved entropy and sortability characteristics.
UUIDs can be generated as atoms, lists of characters, or lists of character codes.
See also the cuid2, ksuid, ids, nanoid, snowflakeid, and ulid libraries.
API documentation
Open the [../../apis/library_index.html#uuid](../../apis/library_index.html#uuid) link in a web browser.
Loading
To load all entities in this library, load the loader.lgt file:
| ?- logtalk_load(uuid(loader)).
Testing
To test this library predicates, load the tester.lgt file:
| ?- logtalk_load(uuid(tester)).
Generating version 1 UUIDs
By default, version 1 UUIDs are generated as atoms. For example:
| ?- uuid::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
UUID = '00a66fc0-82cf-11eb-bc83-f2d19094dc4b'
yes
To generate a UUID using a list of characters representation, use instead the uuid/1 parametric object:
uuid(chars)::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
UUID = ['0','0',d,e,'9','0',c,'0',-,'8','2',c,f,-,'1','1',e,b,-,
a,'9','8','5',-,f,'2',d,'1','9','0','9','4',d,c,'4',b]
yes
Similarly, to get a UUID using a list of character codes representation:
uuid(codes)::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
UUID = [48,48,52,99,99,54,99,48,45,56,50,99,102,45,49,49,101,98,45,
98,57,102,52,45,102,50,100,49,57,48,57,52,100,99,52,98]
yes
Generating version 4 UUIDs
By default, version 4 UUIDs are generated as atoms. For example:
| ?- uuid::uuid_v4(UUID).
UUID = '1c652782-69c5-4252-88c8-09e576a44db5'
yes
To generate a UUID using a list of characters representation, use instead the uuid/1 parametric object:
uuid(chars)::uuid_v4(UUID).
UUID = [d,'3',d,'3','3','5','1','3',-,'8','1',e,c,-,'4',d,'2','6',-,
'9',f,'2','2',-,e,d,'9','5',e,'0','0',e,'1','5','7','0']
yes
Similar to get a UUID using a list of character codes representation:
uuid(codes)::uuid_v4(UUID).
UUID = [102,97,52,54,57,98,100,50,45,51,57,54,51,45,52,97,100,55,45,
98,50,50,55,45,101,100,52,99,56,55,99,54,53,55,102,98]
yes
Generating version 7 UUIDs
Version 7 UUIDs are time-ordered using the Unix Epoch timestamp in milliseconds (as specified in RFC 9562). By default, version 7 UUIDs are generated as atoms. For example:
| ?- uuid::uuid_v7(UUID).
UUID = '018d5f3c-9b5a-7c4e-8f2a-1b3c4d5e6f70'
yes
To generate a UUID using a list of characters representation, use instead the uuid/1 parametric object:
uuid(chars)::uuid_v7(UUID).
UUID = ['0','1','8',d,'5',f,'3',c,-,'9',b,'5',a,-,'7',c,'4',e,-,
'8',f,'2',a,-,'1',b,'3',c,'4',d,'5',e,'6',f,'7','0']
yes
Similar to get a UUID using a list of character codes representation:
uuid(codes)::uuid_v7(UUID).
UUID = [48,49,56,100,53,102,51,99,45,57,98,53,97,45,55,99,52,101,45,
56,102,50,97,45,49,98,51,99,52,100,53,101,54,102,55,48]
yes
Generating the Nil and Max UUIDs
Predicates are also provided that return the Nil and Max UUIDs:
| ?- uuid::uuid_nil(UUID).
UUID = '00000000-0000-0000-0000-000000000000'
yes
| ?- uuid::uuid_max(UUID).
UUID = 'FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF'
yes