Example code fails to build?

[Josh Vander Hook]

I've been using statrs for some poisson testing, and it's fine.

https://github.com/jodavaho/poisson-rate-test/blob/main/src/lib.rs#L110

            let maximum_likelihood_unconstrained:f64 = 
                Poisson::new(obs_rate_one * t_one ).unwrap().pmf(num_events_one as u64)
                * Poisson::new(obs_rate_two * t_two ).unwrap().pmf(num_events_two as u64);

But now I need to use sample. Trying to compile the sample example code in the above (working) library makes it fail to build.

Here's a minimal example that also fails in the same way (you may recognize this as the example code from the documentation).

use rand::distributions::Distribution;
use statrs::distribution::Normal;


fn main() {
    let mut r = rand::thread_rng();
    let n = Normal::new(0.0, 1.0).unwrap();
    for _ in 0..10 {
        print!("{}", n.sample(&mut r));
    }
}

fails:

error[E0599]: no method named `sample` found for struct `statrs::distribution::Normal` in the current scope
 --> src/bin/docs_example.rs:9:24
  |
9 |         print!("{}", n.sample(&mut r));
  |                        ^^^^^^ method not found in `statrs::distribution::Normal`
  |
  = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
  |
1 | use rand::distributions::Distribution;
  |

warning: unused import: `rand::distributions::Distribution`
 --> src/bin/docs_example.rs:1:5
  |
1 | use rand::distributions::Distribution;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

The combination of "unused import for X" and "missing import: X" is really strange.

So, I've tried (in a new package) every code example I could find and none compile as instructed. I'm copy-pasting, but I do have to add main wrappers.

See here: https://github.com/jodavaho/statrs-test/tree/main/src/bin

In particular, Cargo.toml

[package]
name = "statrs-test"
version = "0.1.0"
authors = ["Josh"]
edition = "2018"

[dependencies]
statrs = "*"
# statrs = "0.13"
rand = "0.8.3"

Any thoughts on what is going on?

[Vinzent Steinberg]

Looks like a crate version mismatch. statrs only supports Rand 0.7, but you are trying to use it with Rand 0.8. The Distribution trait you are importing is distinct from the Distribution trait statrs is using (because they are from different rand crates), hence the unused import warning. (Unfortunately, the compiler message is confusing, because it does not tell you that it's talking about two different rand crates.)

cargo tree can help you to debug such problems.

[Josh Vander Hook]

Oh, I'm re-opening to show a workaround that got things to compile for me:
https://stackoverflow.com/q/67510812/389599

This is potentially worth documenting.

[troublescooter]

This is fixed with the new release.