BurntSushi/quickcheck

Gen from seed

jakoschiko opened this issue · 8 comments

jakoschiko commented

Many crates implement quickcheck::Arbitrary and I was very happy that I could use these implementations in dicetest by implementing quickcheck::Gen. Unfortunately I can't do this anymore since quickcheck 1.0.

Would it be possible to provide a function that creates a Gen from a seed? Something like that:

impl Gen {
    pub fn from_seed(seed: u64, size: usize) -> Gen {
        Gen { rng: rand::rngs::SmallRng::seed_from_u64(seed), size: size }
    }
}
BurntSushi commented

That seems sensible to me. I think we should leave off the size parameter perhaps though. I regret that Gen's constructor has it instead of providing a set_size method. So we'll want that when this new constructor is added.

jakoschiko commented

Can I help by creating a PR?

BurntSushi commented
jakoschiko commented

I'm in no hurry, I'll do it within the next days.

ggreif commented

May I suggest from_rng(rng) too? @jakoschiko
I have a supplied random gen from the environment that I have to use.
I tried

    Gen {
	rng: SmallRng::from_rng(rng).unwrap(),
	size: 42,
    }

but got

183 |     rng: SmallRng::from_rng(rng).unwrap(),
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ private field

Maybe just making both fields pub would work? Of course that depends on how settled Gen is...

BurntSushi commented

No. Because that makes rand_core a public dependency.

  • 👍1
jakoschiko commented

@ggreif
rand_core was recently removed from the interface, see #265. I didn't want to discuss this in this issue, I just wanted a replacement. If elegance doesn't matter, you could generate an u64 using rng and pass it to Gen::from_seed. I think SmallRng::from_rng does something similar, but with more bytes.

ggreif commented

Great, a u64 seed is perfectly adequate for my purposes. I am happy without from_rng.