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use smallvec::{Array, SmallVec};
pub type OneVector<T> = SmallVec<[T; 1]>;
pub trait ExpectOne<A: Array> {
fn expect_one(self, err: &'static str) -> A::Item;
}
impl<A: Array> ExpectOne<A> for SmallVec<A> {
fn expect_one(self, err: &'static str) -> A::Item {
assert!(self.len() == 1, err);
self.into_iter().next().unwrap()
}
}
#[cfg(test)]
mod tests {
extern crate test;
use super::*;
#[test]
#[should_panic]
fn test_expect_one_zero() {
let _: isize = OneVector::new().expect_one("");
}
#[test]
#[should_panic]
fn test_expect_one_many() {
OneVector::from_vec(vec![1, 2]).expect_one("");
}
#[test]
fn test_expect_one_one() {
assert_eq!(1, (smallvec![1] as OneVector<_>).expect_one(""));
assert_eq!(1, OneVector::from_vec(vec![1]).expect_one(""));
}
}