Test iterator laziness

Author: Philippe-Cholet

tests/laziness.rs

@@ -0,0 +1,127 @@
+#![allow(unstable_name_collisions, deprecated)]
+
+use std::cell::RefCell;
+use std::collections::BTreeMap;
+
+use itertools::Itertools;
+
+#[test]
+// Force to explicit `let _ = ...;` to help find missing `must_use` attributes manually.
+// Only helpful if you don't add it before seeing if there is an error or not.
+#[deny(unused_must_use)]
+fn laziness() {
+    let used_ids = RefCell::<BTreeMap<_, usize>>::default();
+    let not_lazy = |s: &'static str| -> u8 {
+        *used_ids.borrow_mut().entry(s).or_default() += 1;
+        0
+    };
+    let it = |s: &'static str| (0..20).map(move |_| not_lazy(s));
+    // Itertools trait:
+    let _ = it("interleave-1").interleave(it("interleave-2"));
+    let _ = it("interleave_shortest-1").interleave_shortest(it("interleave_shortest-2"));
+    let _ = it("intersperse").intersperse(0);
+    let _ = it("intersperse_with").intersperse_with(|| 0);
+    let _ = it("zip_longest-1").zip_longest(it("zip_longest-2"));
+    let _ = it("zip_eq-1").zip_eq(it("zip_eq-2"));
+    let _ = it("batching").batching(Iterator::next);
+    let _ = it("group_by").group_by(|x| *x);
+    let _ = it("chunks-1").chunks(1);
+    let _ = it("chunks-2").chunks(2);
+    let _ = it("tuple_windows::<(_,)>").tuple_windows::<(_,)>();
+    let _ = it("tuple_windows::<(_,_)>").tuple_windows::<(_, _)>();
+    let _ = it("tuple_windows::<(_,_,_)>").tuple_windows::<(_, _, _)>();
+    let _ = it("circular_tuple_windows::<(_,)>").circular_tuple_windows::<(_,)>();
+    let _ = it("circular_tuple_windows::<(_,_)>").circular_tuple_windows::<(_, _)>();
+    let _ = it("circular_tuple_windows::<(_,_,_)>").circular_tuple_windows::<(_, _, _)>();
+    let _ = it("tuples::<(_,)>").tuples::<(_,)>();
+    let _ = it("tuples::<(_,_)>").tuples::<(_, _)>();
+    let _ = it("tuples::<(_,_,_)>").tuples::<(_, _, _)>();
+    let (_, _) = it("tee").tee();
+    let _ = it("step").step(2);
+    let _ = it("map_into").map_into::<u16>();
+    let _ = it("map_ok").map(Ok::<u8, ()>).map_ok(|x| x + 1);
+    let _ = it("filter_ok").map(Ok::<u8, ()>).filter_ok(|x| x % 2 == 0);
+    let _ = it("filter_map_ok").map(Ok::<u8, ()>).filter_map_ok(|x| {
+        if x % 2 == 0 {
+            Some(x + 1)
+        } else {
+            None
+        }
+    });
+    let _ = it("flatten_ok").map(|x| Ok::<_, ()>([x])).flatten_ok();
+    let _ = it("merge-1").merge(it("merge-2"));
+    let _ = it("merge_by-1").merge_by(it("merge_by-2"), |_, _| true);
+    let _ = it("merge_join_by:bool-1").merge_join_by(it("merge_join_by:bool-2"), |_, _| true);
+    let _ = it("merge_join_by:Ordering-1").merge_join_by(it("merge_join_by:Ordering-2"), Ord::cmp);
+    let _ = it("kmerge").map(|_| it("kmerge-nested")).kmerge();
+    let _ = it("kmerge_by")
+        .map(|_| it("kmerge_by-nested"))
+        .kmerge_by(|_, _| true);
+    let _ = it("cartesian_product-1").cartesian_product(it("cartesian_product-2"));
+    let _ = vec![
+        it("multi_cartesian_product-1"),
+        it("multi_cartesian_product-2"),
+        it("multi_cartesian_product-3"),
+    ]
+    .into_iter()
+    .multi_cartesian_product();
+    let _ = it("coalesce").coalesce(|x, y| if x == y { Ok(x) } else { Err((x, y)) });
+    let _ = it("dedup").dedup();
+    let _ = it("dedup_by").dedup_by(|_, _| true);
+    let _ = it("dedup_with_count").dedup_with_count();
+    let _ = it("dedup_by_with_count").dedup_by_with_count(|_, _| true);
+    let _ = it("duplicates").duplicates();
+    let _ = it("duplicates_by").duplicates_by(|x| *x);
+    let _ = it("unique").unique();
+    let _ = it("unique_by").unique_by(|x| *x);
+    let _ = it("peeking_take_while")
+        .peekable()
+        .peeking_take_while(|x| x % 2 == 0);
+    let _ = it("take_while_ref").take_while_ref(|x| x % 2 == 0);
+    let _ = it("take_while_inclusive").take_while_inclusive(|x| x % 2 == 0);
+    let _ = it("while_some").map(Some).while_some();
+    let _ = it("tuple_combinations::<(_,)>").tuple_combinations::<(_,)>();
+    let _ = it("tuple_combinations::<(_,_)>").tuple_combinations::<(_, _)>();
+    let _ = it("tuple_combinations::<(_,_,_)>").tuple_combinations::<(_, _, _)>();
+    let _ = it("combinations(0)").combinations(0);
+    let _ = it("combinations(1)").combinations(1);
+    let _ = it("combinations(2)").combinations(2);
+    let _ = it("combinations(3)").combinations(3);
+    it("combinations_with_replacement(0)").combinations_with_replacement(0);
+    it("combinations_with_replacement(1)").combinations_with_replacement(1);
+    it("combinations_with_replacement(2)").combinations_with_replacement(2);
+    it("combinations_with_replacement(3)").combinations_with_replacement(3);
+    let _ = it("permutations(0)").permutations(0);
+    let _ = it("permutations(1)").permutations(1);
+    let _ = it("permutations(2)").permutations(2);
+    let _ = it("permutations(3)").permutations(3);
+    let _ = it("powerset").powerset();
+    let _ = it("pad_using").pad_using(25, |_| 10);
+    let _ = it("with_position").with_position();
+    let _ = it("positions").positions(|v| v % 2 == 0);
+    let _ = it("update").update(|n| *n += 1);
+    it("multipeek").multipeek();
+    // Not iterator themselves but still lazy.
+    let _ = it("into_grouping_map")
+        .map(|x| (x, x + 1))
+        .into_grouping_map();
+    let _ = it("into_grouping_map_by").into_grouping_map_by(|x| *x);
+    // Macros:
+    let _ = itertools::iproduct!(it("iproduct-1"));
+    let _ = itertools::iproduct!(it("iproduct-2"), it("iproduct-3"));
+    let _ = itertools::iproduct!(it("iproduct-4"), it("iproduct-5"), it("iproduct-6"));
+    let _ = itertools::izip!(it("izip-1"));
+    let _ = itertools::izip!(it("izip-2"), it("izip-3"));
+    let _ = itertools::izip!(it("izip-4"), it("izip-5"), it("izip-6"));
+    let _ = itertools::chain!(it("chain-1"));
+    let _ = itertools::chain!(it("chain-2"), it("chain-3"));
+    let _ = itertools::chain!(it("chain-4"), it("chain-5"), it("chain-6"));
+    // Free functions:
+    let _ = itertools::multizip((it("multizip-1"), it("multizip-2")));
+    itertools::put_back(it("put_back"));
+    itertools::put_back(it("put_back")).with_value(15);
+    itertools::peek_nth(it("peek_nth"));
+    itertools::put_back_n(it("put_back_n"));
+    itertools::rciter(it("rciter"));
+    assert!(used_ids.borrow().is_empty(), "{:#?}", used_ids.borrow());
+}