Add example for initializing a PCG RNG

[vks]

No description provided.

[vks]

@kornelski Does this address your concerns?

[vks]

Some tests fail:

error[E0432]: unresolved import `rand`
 --> rand_pcg/src/lib.rs:37:5
  |
5 | use rand::{SeedableRng, Rng};
  |     ^^^^ use of undeclared crate or module `rand`

error[E0599]: no function or associated item named `from_entropy` found for struct `Mcg128Xsl64` in the current scope
 --> rand_pcg/src/lib.rs:40:25
  |
8 | let mut rng = Pcg64Mcg::from_entropy();
  |                         ^^^^^^^^^^^^ function or associated item not found in `Mcg128Xsl64`

Not sure what the best fix is. We could use rand_core and seed_from_u64 instead.

[kornelski]

Yes, thank you!

[dhardy]

error[E0432]: unresolved import rand

Indeed, this makes examples in RNG crates a pain.

For this RNG I think we should mention seed_from_u64 anyway since its main use-cases probably involve reproducible seeding. We can include a comment like:

let mut rng = Pcg64Mcg::seed_from_u64(0);
// Alternative: Pcg64Mcg::from_entropy();

[newpavlov]

Indeed, this makes examples in RNG crates a pain.

I think it can be fixed by adding rand as a dev dependency.

[vks]

@newpavlov Would you prefer this to the current solution (seed_from_u64 and next_u64)?

[newpavlov]

I am fine with either, but the docs probably should mention that the crate functionality is implemented using traits from the rand_core trait and extended further by the rand crate.

[vks]

@newpavlov I added an example for using rand (adding it as a dev dependency).