Implement direct usize indexing

src/map.rs

@@ -993,6 +993,28 @@ impl<K, V, S> IntoIterator for IndexMap<K, V, S> {
     }
 }
 
+/// Access `IndexMap` values corresponding to a key.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map["lorem"], "LOREM");
+/// assert_eq!(map["ipsum"], "IPSUM");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map["bar"]); // panics!
+/// ```
 impl<K, V, Q: ?Sized, S> Index<&Q> for IndexMap<K, V, S>
 where
     Q: Hash + Equivalent<K>,
@@ -1001,28 +1023,138 @@ where
 {
     type Output = V;
 
+    /// Returns a reference to the value corresponding to the supplied `key`.
+    ///
     /// ***Panics*** if `key` is not present in the map.
     fn index(&self, key: &Q) -> &V {
         self.get(key).expect("IndexMap: key not found")
     }
 }
 
+/// Access `IndexMap` values corresponding to a key.
+///
 /// Mutable indexing allows changing / updating values of key-value
 /// pairs that are already present.
 ///
 /// You can **not** insert new pairs with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map["lorem"];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map["bar"] = 1; // panics!
+/// ```
 impl<K, V, Q: ?Sized, S> IndexMut<&Q> for IndexMap<K, V, S>
 where
     Q: Hash + Equivalent<K>,
     K: Hash + Eq,
     S: BuildHasher,
 {
+    /// Returns a mutable reference to the value corresponding to the supplied `key`.
+    ///
     /// ***Panics*** if `key` is not present in the map.
     fn index_mut(&mut self, key: &Q) -> &mut V {
         self.get_mut(key).expect("IndexMap: key not found")
     }
 }
 
+/// Access `IndexMap` values at indexed positions.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map[0], "LOREM");
+/// assert_eq!(map[1], "IPSUM");
+/// map.reverse();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "SIT");
+/// map.sort_keys();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "DOLOR");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map[10]); // panics!
+/// ```
+impl<K, V, S> Index<usize> for IndexMap<K, V, S> {
+    type Output = V;
+
+    /// Returns a reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index(&self, index: usize) -> &V {
+        self.get_index(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
+/// Access `IndexMap` values at indexed positions.
+///
+/// Mutable indexing allows changing / updating indexed values
+/// that are already present.
+///
+/// You can **not** insert new values with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map[0];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map[10] = 1; // panics!
+/// ```
+impl<K, V, S> IndexMut<usize> for IndexMap<K, V, S> {
+    /// Returns a mutable reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index_mut(&mut self, index: usize) -> &mut V {
+        self.get_index_mut(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
 impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>
 where
     K: Hash + Eq,

src/set.rs

@@ -11,7 +11,7 @@ use core::cmp::Ordering;
 use core::fmt;
 use core::hash::{BuildHasher, Hash};
 use core::iter::{Chain, FromIterator};
-use core::ops::{BitAnd, BitOr, BitXor, RangeBounds, Sub};
+use core::ops::{BitAnd, BitOr, BitXor, Index, RangeBounds, Sub};
 use core::slice;
 
 use super::{Entries, Equivalent, IndexMap};
@@ -606,6 +606,46 @@ impl<T, S> IndexSet<T, S> {
     }
 }
 
+/// Access `IndexSet` values at indexed positions.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexSet;
+///
+/// let mut set = IndexSet::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     set.insert(word.to_string());
+/// }
+/// assert_eq!(set[0], "Lorem");
+/// assert_eq!(set[1], "ipsum");
+/// set.reverse();
+/// assert_eq!(set[0], "amet");
+/// assert_eq!(set[1], "sit");
+/// set.sort();
+/// assert_eq!(set[0], "Lorem");
+/// assert_eq!(set[1], "amet");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexSet;
+///
+/// let mut set = IndexSet::new();
+/// set.insert("foo");
+/// println!("{:?}", set[10]); // panics!
+/// ```
+impl<T, S> Index<usize> for IndexSet<T, S> {
+    type Output = T;
+
+    /// Returns a reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index(&self, index: usize) -> &T {
+        self.get_index(index)
+            .expect("IndexSet: index out of bounds")
+    }
+}
+
 /// An owning iterator over the items of a `IndexSet`.
 ///
 /// This `struct` is created by the [`into_iter`] method on [`IndexSet`]

tests/quick.rs

@@ -1,4 +1,4 @@
-use indexmap::IndexMap;
+use indexmap::{IndexMap, IndexSet};
 use itertools::Itertools;
 
 use quickcheck::quickcheck;
@@ -163,6 +163,26 @@ quickcheck! {
             elements.iter().all(|k| map.get(k).is_some())
     }
 
+    fn indexing(insert: Vec<u8>) -> bool {
+        let mut map: IndexMap<_, _> = insert.into_iter().map(|x| (x, x)).collect();
+        let set: IndexSet<_> = map.keys().cloned().collect();
+        assert_eq!(map.len(), set.len());
+
+        for (i, &key) in set.iter().enumerate() {
+            assert_eq!(map.get_index(i), Some((&key, &key)));
+            assert_eq!(set.get_index(i), Some(&key));
+            assert_eq!(map[i], key);
+            assert_eq!(set[i], key);
+
+            *map.get_index_mut(i).unwrap().1 >>= 1;
+            map[i] <<= 1;
+        }
+
+        set.iter().enumerate().all(|(i, &key)| {
+            let value = key & !1;
+            map[&key] == value && map[i] == value
+        })
+    }
 }
 
 use crate::Op::*;