get: when is it ESI and/or DEI

Author: Philippe-Cholet

src/lib.rs

@@ -515,8 +515,9 @@ pub trait Itertools: Iterator {
     ///
     /// It's a generalisation of [`Iterator::take`] and [`Iterator::skip`],
     /// and uses these under the hood.
-    /// Therefore, the resulting iterator is [`DoubleEndedIterator`]
-    /// and/or [`ExactSizeIterator`] if the adapted iterator is.
+    /// Therefore, the resulting iterator is:
+    /// - [`ExactSizeIterator`] if the adapted iterator is [`ExactSizeIterator`].
+    /// - [`DoubleEndedIterator`] if the adapted iterator is [`DoubleEndedIterator`] and [`ExactSizeIterator`].
     ///
     /// # Unspecified Behavior
     /// The result of indexing with an exhausted [`core::ops::RangeInclusive`] is unspecified.

tests/test_core.rs

@@ -18,6 +18,28 @@ use crate::it::Itertools;
 use core::iter;
 use itertools as it;
 
+#[allow(dead_code)]
+fn get_esi_then_esi<I: ExactSizeIterator + Clone>(it: I) {
+    fn is_esi(_: impl ExactSizeIterator) {}
+    is_esi(it.clone().get(1..4));
+    is_esi(it.clone().get(1..=4));
+    is_esi(it.clone().get(1..));
+    is_esi(it.clone().get(..4));
+    is_esi(it.clone().get(..=4));
+    is_esi(it.get(..));
+}
+
+#[allow(dead_code)]
+fn get_dei_esi_then_dei_esi<I: DoubleEndedIterator + ExactSizeIterator + Clone>(it: I) {
+    fn is_dei_esi(_: impl DoubleEndedIterator + ExactSizeIterator) {}
+    is_dei_esi(it.clone().get(1..4));
+    is_dei_esi(it.clone().get(1..=4));
+    is_dei_esi(it.clone().get(1..));
+    is_dei_esi(it.clone().get(..4));
+    is_dei_esi(it.clone().get(..=4));
+    is_dei_esi(it.get(..));
+}
+
 #[test]
 fn product0() {
     let mut prod = iproduct!();