vendor/itertools-0.10.1/tests/specializations.rs

use itertools::Itertools;
use std::fmt::Debug;
use quickcheck::quickcheck;

struct Unspecialized<I>(I);
impl<I> Iterator for Unspecialized<I>
where
    I: Iterator,
{
    type Item = I::Item;

    #[inline(always)]
    fn next(&mut self) -> Option<Self::Item> {
        self.0.next()
    }
}

fn check_specialized<'a, V, IterItem, Iter, F>(iterator: &Iter, mapper: F)
where
    V: Eq + Debug,
    Iter: Iterator<Item = IterItem> + Clone + 'a,
    F: Fn(Box<dyn Iterator<Item = IterItem> + 'a>) -> V,
{
    assert_eq!(
        mapper(Box::new(Unspecialized(iterator.clone()))),
        mapper(Box::new(iterator.clone()))
    )
}

fn test_specializations<IterItem, Iter>(
    it: &Iter,
) where
    IterItem: Eq + Debug + Clone,
    Iter: Iterator<Item = IterItem> + Clone,
{
    check_specialized(it, |i| i.count());
    check_specialized(it, |i| i.last());
    check_specialized(it, |i| i.collect::<Vec<_>>());
    check_specialized(it, |i| {
        let mut parameters_from_fold = vec![];
        let fold_result = i.fold(vec![], |mut acc, v: IterItem| {
            parameters_from_fold.push((acc.clone(), v.clone()));
            acc.push(v);
            acc
        });
        (parameters_from_fold, fold_result)
    });
    check_specialized(it, |mut i| {
        let mut parameters_from_all = vec![];
        let first = i.next();
        let all_result = i.all(|x| {
            parameters_from_all.push(x.clone());
            Some(x)==first
        });
        (parameters_from_all, all_result)
    });
    let size = it.clone().count();
    for n in 0..size + 2 {
        check_specialized(it, |mut i| i.nth(n));
    }
    // size_hint is a bit harder to check
    let mut it_sh = it.clone();
    for n in 0..size + 2 {
        let len = it_sh.clone().count();
        let (min, max) = it_sh.size_hint();
        assert_eq!(size - n.min(size), len);
        assert!(min <= len);
        if let Some(max) = max {
            assert!(len <= max);
        }
        it_sh.next();
    }
}

quickcheck! {
    fn put_back_qc(test_vec: Vec<i32>) -> () {
        test_specializations(&itertools::put_back(test_vec.iter()));
        let mut pb = itertools::put_back(test_vec.into_iter());
        pb.put_back(1);
        test_specializations(&pb);
    }
}

quickcheck! {
    fn merge_join_by_qc(i1: Vec<usize>, i2: Vec<usize>) -> () {
        test_specializations(&i1.into_iter().merge_join_by(i2.into_iter(), std::cmp::Ord::cmp));
    }
}

quickcheck! {
    fn map_into(v: Vec<u8>) -> () {
        test_specializations(&v.into_iter().map_into::<u32>());
    }
}

quickcheck! {
    fn map_ok(v: Vec<Result<u8, char>>) -> () {
        test_specializations(&v.into_iter().map_ok(|u| u.checked_add(1)));
    }
}