Track hash Set length

Can be used later to rehash the hash table if it is full up to some
percentage.

source/tanya/container/entry.d

@@ -120,6 +120,7 @@ package struct HashArray(alias hasher, K, V = void)
 
     Array!Bucket array;
     size_t lengthIndex;
+    size_t length;
 
     /*
      * Returns bucket position for `hash`. `0` may mean the 0th position or an
@@ -144,10 +145,15 @@ package struct HashArray(alias hasher, K, V = void)
 
             foreach (ref e; this.array[bucketPosition .. $])
             {
-                if (e == key || e.status != BucketStatus.used)
+                if (e == key)
                 {
                     return e;
                 }
+                else if (e.status != BucketStatus.used)
+                {
+                    ++this.length;
+                    return e;
+                }
             }
 
             if (primes.length == (this.lengthIndex + 1))
@@ -207,4 +213,46 @@ package struct HashArray(alias hasher, K, V = void)
     {
         return this.array.length;
     }
+
+    void clear()
+    {
+        this.array.clear();
+        this.length = 0;
+    }
+
+    size_t remove(ref K value)
+    {
+        auto bucketPosition = locateBucket(value);
+        foreach (ref e; this.array[bucketPosition .. $])
+        {
+            if (e == value) // Found.
+            {
+                e.remove();
+                --this.length;
+                return 1;
+            }
+            else if (e.status == BucketStatus.empty)
+            {
+                break;
+            }
+        }
+        return 0;
+    }
+
+    bool find(ref const K value) const
+    {
+        auto bucketPosition = locateBucket(value);
+        foreach (ref e; this.array[bucketPosition .. $])
+        {
+            if (e == value) // Found.
+            {
+                return true;
+            }
+            else if (e.status == BucketStatus.empty)
+            {
+                break;
+            }
+        }
+        return false;
+    }
 }

source/tanya/container/set.d

@@ -314,15 +314,7 @@ if (is(typeof(hasher(T.init)) == size_t))
      */
     @property size_t length() const
     {
-        size_t count;
-        foreach (ref e; this.data.array[])
-        {
-            if (e.status == BucketStatus.used)
-            {
-                ++count;
-            }
-        }
-        return count;
+        return this.data.length;
     }
 
     ///
@@ -335,6 +327,24 @@ if (is(typeof(hasher(T.init)) == size_t))
         assert(set.length == 1);
     }
 
+    /**
+     * Tells whether the container contains any elements.
+     *
+     * Returns: Whether the container is empty.
+     */
+    @property bool empty() const
+    {
+        return length == 0;
+    }
+
+    /**
+     * Removes all elements.
+     */
+    void clear()
+    {
+        this.data.clear();
+    }
+
     /// The maximum number of buckets the container can have.
     enum size_t maxBucketCount = primes[$ - 1];
 
@@ -386,20 +396,7 @@ if (is(typeof(hasher(T.init)) == size_t))
      */
     size_t remove(T value)
     {
-        auto bucketPosition = this.data.locateBucket(value);
-        foreach (ref e; this.data.array[bucketPosition .. $])
-        {
-            if (e == value) // Found.
-            {
-                e.remove();
-                return 1;
-            }
-            else if (e.status == BucketStatus.empty)
-            {
-                break;
-            }
-        }
-        return 0;
+        return this.data.remove(value);
     }
 
     ///
@@ -427,19 +424,7 @@ if (is(typeof(hasher(T.init)) == size_t))
      */
     bool opBinaryRight(string op : "in")(auto ref const T value) const
     {
-        auto bucketPosition = this.data.locateBucket(value);
-        foreach (ref e; this.data.array[bucketPosition .. $])
-        {
-            if (e == value) // Found.
-            {
-                return true;
-            }
-            else if (e.status == BucketStatus.empty)
-            {
-                break;
-            }
-        }
-        return false;
+        return this.data.find(value);
     }
 
     ///