Remove superfluous backing class for share_obj

I originally wanted to make share_obj a class so that I could hide the
helper function, but it turned out that I needed a function after all
since a function template can be inferred from the parameters but the
type cannot from the constructor.

By returning a shared_ptr directly, the compiler can do return object
optimization.

opm/core/utility/share_obj.hpp

@@ -0,0 +1,49 @@
+/*
+  Copyright (c) 2013 Uni Research AS
+
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  OPM is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with OPM.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef OPM_SHARE_OBJ_HPP
+#define OPM_SHARE_OBJ_HPP
+
+#include <memory>  // shared_ptr
+
+namespace Opm {
+
+/// Custom deleter that does nothing
+inline void no_delete (void const *) { }
+
+/*!
+ * Share pointer of a local object.
+ *
+ * Use this wrapper when an interface needs a shared_ptr, but you
+ * want to pass an object that has local storage (and you know
+ * that the shared_ptr client doesn't need it outside of the scope).
+ *
+ * \example
+ * \code{.cpp}
+ *  Foo obj;
+ *  std::shared_ptr <Foo> ptr = share_obj (obj);
+ * \endcode
+ */
+template <typename T> std::shared_ptr <T> share_obj (T& t) {
+    return std::shared_ptr <T> (&t, no_delete);
+}
+
+} // namespace Opm
+
+#endif /* OPM_SHARE_OBJ_HPP */