Add algorithm.searching.count

source/tanya/algorithm/searching.d

@@ -0,0 +1,78 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Searching algorithms.
+ *
+ * Copyright: Eugene Wissner 2018.
+ * License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
+ *                  Mozilla Public License, v. 2.0).
+ * Authors: $(LINK2 mailto:info@caraus.de, Eugene Wissner)
+ * Source: $(LINK2 https://github.com/caraus-ecms/tanya/blob/master/source/tanya/algorithm/searching.d,
+ *                 tanya/algorithm/searching.d)
+ */
+module tanya.algorithm.searching;
+
+import tanya.range;
+
+/**
+ * Counts the elements in an input range.
+ *
+ * If $(D_PARAM R) has length, $(D_PSYMBOL count) returns it, otherwise it
+ * iterates over the range and counts the elements.
+ *
+ * Params:
+ *  R     = Input range type.
+ *  range = Input range.
+ *
+ * Returns: $(D_PARAM range) length.
+ */
+size_t count(R)(R range)
+if (isInputRange!R)
+{
+    static if (hasLength!R)
+    {
+        return range.length;
+    }
+    else
+    {
+        size_t counter;
+        for (; !range.empty; range.popFront(), ++counter)
+        {
+        }
+        return counter;
+    }
+}
+
+///
+@nogc nothrow pure @safe unittest
+{
+    int[3] array;
+    assert(count(array) == 3);
+}
+
+@nogc nothrow pure @safe unittest
+{
+    static struct Range
+    {
+        private int counter = 3;
+
+        int front() const @nogc nothrow pure @safe
+        {
+            return this.counter;
+        }
+
+        void popFront() @nogc nothrow pure @safe
+        {
+            --this.counter;
+        }
+
+        bool empty() const @nogc nothrow pure @safe
+        {
+            return this.counter == 0;
+        }
+    }
+    Range range;
+    assert(count(range) == 3);
+}