Add functional module. Fix #52

source/tanya/functional.d

@@ -0,0 +1,71 @@
+/* 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/. */
+
+/**
+ * Functions that manipulate other functions and their argument lists.
+ *
+ * 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/functional.d,
+ *                 tanya/functional.d)
+ */
+module tanya.functional;
+
+import tanya.algorithm.mutation;
+import tanya.meta.metafunction;
+
+private template forwardOne(alias arg)
+{
+    static if (__traits(isRef, arg) || __traits(isOut, arg))
+    {
+        alias forwardOne = arg;
+    }
+    else
+    {
+        @property auto forwardOne()
+        {
+            return move(arg);
+        }
+    }
+}
+
+/**
+ * Forwards its argument list preserving $(D_KEYWORD ref) and $(D_KEYWORD out)
+ * storage classes.
+ *
+ * $(D_PSYMBOL forward) accepts a list of variables or literals. It returns an
+ * argument list of the same length that can be for example passed to a
+ * function accepting the arguments of this type.
+ *
+ * Params:
+ *  args = Argument list.
+ *
+ * Returns: $(D_PARAM args) with their original storage classes.
+ */
+template forward(args...)
+{
+    static if (args.length == 1)
+    {
+        alias forward = forwardOne!(args[0]);
+    }
+    else
+    {
+        alias forward = Map!(forwardOne, args);
+    }
+}
+
+///
+@nogc nothrow pure @safe unittest
+{
+    static assert(is(typeof((int i) { int v = forward!i; })));
+    static assert(is(typeof((ref int i) { int v = forward!i; })));
+    static assert(is(typeof({
+        void f(int i, ref int j, out int k)
+        {
+            f(forward!(i, j, k));
+        }
+    })));
+}