From 1f69c5347ec6e353f0ca63f125a144b797450e58 Mon Sep 17 00:00:00 2001
From: YizhePKU <yizhe@pku.edu.cn>
Date: Wed, 3 Jan 2024 05:02:35 +0000
Subject: [PATCH] `multi_cartesian_product`: document the nullary product

Regression test for #337
---
 src/lib.rs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/lib.rs b/src/lib.rs
index 126eb2221..1f39379e2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1181,6 +1181,16 @@ pub trait Itertools: Iterator {
     /// assert_eq!(multi_prod.next(), Some(vec![1, 3, 5]));
     /// assert_eq!(multi_prod.next(), None);
     /// ```
+    ///
+    /// If the adapted iterator is empty, the result is an iterator yielding a single empty vector.
+    /// This is known as the [nullary cartesian product](https://en.wikipedia.org/wiki/Empty_product#Nullary_Cartesian_product).
+    ///
+    /// ```
+    /// use itertools::Itertools;
+    /// let mut nullary_cartesian_product = (0..0).map(|i| (i * 2)..(i * 2 + 2)).multi_cartesian_product();
+    /// assert_eq!(nullary_cartesian_product.next(), Some(vec![]));
+    /// assert_eq!(nullary_cartesian_product.next(), None);
+    /// ```
     #[cfg(feature = "use_alloc")]
     fn multi_cartesian_product(self) -> MultiProduct<<Self::Item as IntoIterator>::IntoIter>
     where