Math: added header with tags.

Will be used to distinguish various kinds of construction.

src/Magnum/Math/CMakeLists.txt

@@ -41,6 +41,7 @@ set(MagnumMath_HEADERS
     Range.h
     RectangularMatrix.h
     Swizzle.h
+    Tags.h
     Unit.h
     Vector.h
     Vector2.h

src/Magnum/Math/Tags.h

@@ -0,0 +1,66 @@
+#ifndef Magnum_Math_Tags_h
+#define Magnum_Math_Tags_h
+/*
+    This file is part of Magnum.
+
+    Copyright © 2010, 2011, 2012, 2013, 2014, 2015
+              Vladimír Vondruš <mosra@centrum.cz>
+
+    Permission is hereby granted, free of charge, to any person obtaining a
+    copy of this software and associated documentation files (the "Software"),
+    to deal in the Software without restriction, including without limitation
+    the rights to use, copy, modify, merge, publish, distribute, sublicense,
+    and/or sell copies of the Software, and to permit persons to whom the
+    Software is furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included
+    in all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+    THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+    DEALINGS IN THE SOFTWARE.
+*/
+
+/** @file
+ * @brief Tag type @ref Magnum::Math::ZeroInitT, @ref Magnum::Math::IdentityInitT, tag @ref Magnum::Math::ZeroInit, @ref Magnum::Math::IdentityInit
+ */
+
+namespace Magnum { namespace Math {
+
+/**
+@brief Zero initialization tag type
+
+Used to distinguish construction with all elements set to zero.
+@see @ref ZeroInit
+*/
+struct ZeroInitT {};
+
+/**
+@brief Identity initialization tag type
+
+Used to distinguish construction with transformation set to identity.
+@see @ref IdentityInit
+*/
+struct IdentityInitT {};
+
+/**
+@brief Zero initialization tag
+
+Use for construction with all elements set to zero.
+*/
+constexpr ZeroInitT ZeroInit{};
+
+/**
+@brief Identity initialization tag
+
+Use for construction with transformation set to identity.
+*/
+constexpr IdentityInitT IdentityInit{};
+
+}}
+
+#endif