functor: add construct and tuple_construct

functor.hpp

@@ -3,12 +3,13 @@
  * 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/.
  *
- * Copyright 2018 Danny Robson <danny@nerdcruft.net>
+ * Copyright 2018-2019 Danny Robson <danny@nerdcruft.net>
  */
 
 #pragma once
 
 #include <utility>
+#include <tuple>
 
 
 namespace cruft::functor {
@@ -69,4 +70,33 @@ namespace cruft::functor {
     //-------------------------------------------------------------------------
     template <typename ValueT>
     constant (ValueT) -> constant<std::decay_t<ValueT>>;
-};
+
+
+    ///////////////////////////////////////////////////////////////////////////
+    /// Returns a ValueT constructed from the supplied arguments.
+    template <typename ValueT>
+    struct construct {
+        template <typename ...Args>
+        ValueT operator() (Args &&...args)
+        {
+            return ValueT {
+                std::forward<Args> (args)...
+            };
+        }
+    };
+
+
+    ///------------------------------------------------------------------------
+    /// Returns a ValueT constructed from a tuple of arguments.
+    template <typename ValueT>
+    struct tuple_construct {
+        template <typename Args>
+        ValueT operator() (Args &&args)
+        {
+            return std::apply (
+                construct<ValueT> {},
+                std::forward<Args> (args)
+            );
+        }
+    };
+}