docs.rs failed to build slice_trait-0.3.15
Please check the build logs for more information.
See Builds for ideas on how to fix a failed build, or Metadata for how to configure docs.rs builds.
If you believe this is docs.rs' fault, open an issue.

use slice_trait::*;

let a: &[i32] = [1, 2, 3].as_slice();

fn first<'a, S: Slice + ?Sized>(slice: &'a S) -> Option<&'a S::Item>
where
    S::Item: Copy,
{
    slice.as_slice().first()
}

assert_eq!(first(a), Some(&1));