Support V4 Uuids from arbitrary random bytes

[KodrAus]

Note: for support questions, please use gitter or users forums. This
repository's issues are reserved for feature requests and bug reports.

I'm submitting a ...

• bug report
• feature request
• support request => Please do not submit support request here, see note
  at the top of this template.

Description

I thought we could flesh out our solution to creating uuids using alternative Rngs without having to make rand a public dependency.

new_v4_bat_scooter_name_not_important

servo/servo#20306 suggested a new_v4_from_bytes method as a workaround to needing to make rand a public dependency. Following the naming convention for other constructors, it might look like:

fn new_v4_from_bytes(b: &[u8]) -> Result<Uuid, ParseError>;

let uuid = Uuid::new_v4_from_bytes(b).expect("invalid length");

It would be nice to use [u8; 16] as the source instead of &[u8] so we can make the method infallible. It would be a bit inconsistent to use fn new_v4_from_bytes(b: [u8; 16]) since we already have fn from_bytes(b: &[u8]). new_v4_from_uuid_bytes is a bit of a nasty name. So for now it could be:

fn new_v4_bat_scooter_name_not_important(b: [u8; 16]) -> Uuid;

let uuid = Uuid::new_v4_bat_scooter_name_not_important(b);

We could even go ahead and name it something like new_v4_from_rng_bytes([u8; 16]) and deprecate it once rand is stable in favour of Rand::rand.

Builder

Edit: Moved to a seperate issue #171

Related to: #153

cc: @nox @kinggoesgaming @Dylan-DPC

[kinggoesgaming]

We could even go ahead and name it something like new_v4_from_rng_bytes([u8; 16]) and deprecate it once rand is stable in favour of Rand::rand.

I like this name, as it clearly gets the meaning across.

Edit: removed suggestion on using #[unstable] attribute.

---

As per the Builder I think I will give it some thought before giving any comments on it.

[nox]

I would use random instead of rng in the name. What do you mean by #[unstable]?

[kinggoesgaming]

wait nevermind, ignore that #[unstable] I sometimes forget that unstable is std specific attribute

[Dylan-DPC-zz]

Will give it a try today :)

Edit: Have moved Builder Pattern to a seperate issue #171

[kinggoesgaming]

done