Added thirdparty: boost library

thirdparty/include/boost/hana/fwd/index_if.hpp

@@ -0,0 +1,60 @@
+/*!
+@file
+Forward declares `boost::hana::index_if`.
+
+Copyright Louis Dionne 2013-2022
+Copyright Jason Rice 2017
+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_INDEX_IF_HPP
+#define BOOST_HANA_FWD_INDEX_IF_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+namespace boost { namespace hana {
+    //! Finds the value associated to the first key satisfying a predicate.
+    //! @ingroup group-Iterable
+    //!
+    //! Given an `Iterable` structure `xs` and a predicate `pred`,
+    //! `index_if(xs, pred)` returns a `hana::optional` containing an `IntegralConstant`
+    //! of the index of the first element that satisfies the predicate or nothing
+    //! if no element satisfies the predicate.
+    //!
+    //!
+    //! @param xs
+    //! The structure to be searched.
+    //!
+    //! @param predicate
+    //! A function called as `predicate(x)`, where `x` is an element of the
+    //! `Iterable` structure and returning whether `x` is the element being
+    //! searched for. In the current version of the library, the predicate
+    //! has to return an `IntegralConstant` holding a value that can be
+    //! converted to `bool`.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/index_if.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto index_if = [](auto&& xs, auto&& predicate) {
+        return tag-dispatched;
+    };
+#else
+    template <typename S, typename = void>
+    struct index_if_impl : index_if_impl<S, when<true>> { };
+
+    struct index_if_t {
+        template <typename Xs, typename Pred>
+        constexpr auto operator()(Xs&& xs, Pred&& pred) const;
+    };
+
+    BOOST_HANA_INLINE_VARIABLE constexpr index_if_t index_if{};
+#endif
+}} // end namespace boost::hana
+
+#endif // !BOOST_HANA_FWD_INDEX_IF_HPP
+