Added thirdparty: boost library

thirdparty/include/boost/hana/fwd/concept/integral_constant.hpp

@@ -0,0 +1,73 @@
+/*!
+@file
+Forward declares `boost::hana::IntegralConstant`.
+
+Copyright Louis Dionne 2013-2022
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+ */
+
+#ifndef BOOST_HANA_FWD_CONCEPT_INTEGRAL_CONSTANT_HPP
+#define BOOST_HANA_FWD_CONCEPT_INTEGRAL_CONSTANT_HPP
+
+#include <boost/hana/config.hpp>
+
+
+namespace boost { namespace hana {
+    //! @ingroup group-concepts
+    //! The `IntegralConstant` concept represents compile-time integral values.
+    //!
+    //! The `IntegralConstant` concept represents objects that hold a
+    //! `constexpr` value of an integral type. In other words, it describes
+    //! the essential functionality provided by `std::integral_constant`.
+    //! An `IntegralConstant` is also just a special kind of `Constant`
+    //! whose inner value is of an integral type.
+    //!
+    //!
+    //! Minimal complete definition
+    //! ---------------------------
+    //! The requirements for being an `IntegralConstant` are quite simple.
+    //! First, an `IntegralConstant` `C` must be a `Constant` such that
+    //! `Tag::value_type` is an integral type, where `Tag` is the tag of `C`.
+    //!
+    //! Secondly, `C` must have a nested `static constexpr` member named
+    //! `value`, such that the following code is valid:
+    //! @code
+    //!     constexpr auto v = C::value;
+    //! @endcode
+    //! Because of the requirement that `Tag::value_type` be an integral type,
+    //! it follows that `C::value` must be an integral value.
+    //!
+    //! Finally, it is necessary to specialize the `IntegralConstant` template
+    //! in the `boost::hana` namespace to tell Hana that a type is a model
+    //! of `IntegralConstant`:
+    //! @code
+    //!     namespace boost { namespace hana {
+    //!         template <>
+    //!         struct IntegralConstant<your_custom_tag> {
+    //!             static constexpr bool value = true;
+    //!         };
+    //!     }}
+    //! @endcode
+    //!
+    //!
+    //! Refined concept
+    //! ---------------
+    //! 1. `Constant` (free implementation of `value`)\n
+    //! The `value` function required to be a `Constant` can be implemented
+    //! as follows for `IntegralConstant`s:
+    //! @code
+    //!     value<C>() == C::value
+    //! @endcode
+    //! The `to` function must still be provided explicitly for the model
+    //! of `Constant` to be complete.
+    //!
+    //!
+    //! Concrete models
+    //! ---------------
+    //! `hana::integral_constant`
+    template <typename C>
+    struct IntegralConstant;
+}} // end namespace boost::hana
+
+#endif // !BOOST_HANA_FWD_CONCEPT_INTEGRAL_CONSTANT_HPP