# `uuid`

This library implements a Universally unique identifier (UUID) generator. Currently only version 1 and version 4 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 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.

UUIDs can be generated as atoms, lists of characters, or lists of character codes.

See also the `ids` and `ulid` libraries.

## API documentation

Open the ../../docs/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

Similar 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 the null UUID

A predicate is also provided that returns the null UUID:

    | ?- uuid::uuid_null(UUID).
    UUID = '00000000-0000-0000-0000-000000000000'
    yes