Make with_hasher const

Author: mwillsey

src/map.rs

@@ -166,10 +166,7 @@ impl<K, V, S> IndexMap<K, V, S> {
     #[inline]
     pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self {
         if n == 0 {
-            IndexMap {
-                core: IndexMapCore::new(),
-                hash_builder,
-            }
+            Self::with_hasher(hash_builder)
         } else {
             IndexMap {
                 core: IndexMapCore::with_capacity(n),
@@ -179,8 +176,11 @@ impl<K, V, S> IndexMap<K, V, S> {
     }
 
     /// Create a new map with `hash_builder`
-    pub fn with_hasher(hash_builder: S) -> Self {
-        Self::with_capacity_and_hasher(0, hash_builder)
+    pub const fn with_hasher(hash_builder: S) -> Self {
+        IndexMap {
+            core: IndexMapCore::new(),
+            hash_builder,
+        }
     }
 
     /// Computes in **O(1)** time.

src/map/core.rs

@@ -120,7 +120,7 @@ impl<K, V> Entries for IndexMapCore<K, V> {
 
 impl<K, V> IndexMapCore<K, V> {
     #[inline]
-    pub(crate) fn new() -> Self {
+    pub(crate) const fn new() -> Self {
         IndexMapCore {
             indices: RawTable::new(),
             entries: Vec::new(),

src/set.rs

@@ -156,7 +156,7 @@ impl<T, S> IndexSet<T, S> {
     }
 
     /// Create a new set with `hash_builder`
-    pub fn with_hasher(hash_builder: S) -> Self {
+    pub const fn with_hasher(hash_builder: S) -> Self {
         IndexSet {
             map: IndexMap::with_hasher(hash_builder),
         }