Merge pull request #40 from chris-ha458/with_capacity

With capacity

src/impls/create.rs

@@ -17,6 +17,18 @@ where
             zero: N::zero(),
         }
     }
+
+    /// Create a new, empty `Counter` with the specified capacity.
+    ///
+    /// Note that `capacity` in this case indicates how many distinct items may be counted without reallocation.
+    /// It is not related to the total number of items which may be counted.
+    /// For example, `"aaa"` requires a capacity of 1. `"abc"` requires a capacity of 3.
+    pub fn with_capacity(capacity: usize) -> Self {
+        Counter {
+            map: HashMap::with_capacity(capacity),
+            zero: N::zero(),
+        }
+    }
 }
 
 impl<T, N> Default for Counter<T, N>

src/unit_tests.rs

@@ -12,6 +12,13 @@ fn test_creation() {
     expected.insert(&ONE, 1);
     assert!(counter.map == expected);
 }
+
+#[test]
+fn test_creation_with_capacity() {
+    let counter: Counter<usize, usize> = Counter::with_capacity(3);
+    assert_eq!(counter.map.capacity(), 3);
+}
+
 #[test]
 fn test_update() {
     let mut counter = "abbccc".chars().collect::<Counter<_>>();