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+/*!
+@file
+Forward declares `boost::hana::adjust_if`.
+
+@copyright Louis Dionne 2013-2016
+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_ADJUST_IF_HPP
+#define BOOST_HANA_FWD_ADJUST_IF_HPP
+
+#include <boost/hana/config.hpp>
+#include <boost/hana/core/when.hpp>
+
+
+BOOST_HANA_NAMESPACE_BEGIN
+    //! Apply a function on all the elements of a structure satisfying a predicate.
+    //! @ingroup group-Functor
+    //!
+    //! Given a Functor, a predicate `pred` and a function `f`, `adjust_if`
+    //! will _adjust_ the elements of the Functor that satisfy the predicate
+    //! with the function `f`. In other words, `adjust_if` will return a new
+    //! Functor equal to the original one, except that the elements satisfying
+    //! the predicate will be transformed with the given function. Elements
+    //! for which the predicate is not satisfied are left untouched, and they
+    //! are kept as-is in the resulting Functor.
+    //!
+    //!
+    //! Signature
+    //! ---------
+    //! Given a `Functor` `F` and a `Logical` `Bool`, the signature is
+    //! \f$
+    //!     \mathtt{adjust_if} : F(T) \times (T \to Bool) \times (T \to T) \to F(T)
+    //! \f$
+    //!
+    //! @param xs
+    //! The structure to adjust with `f`.
+    //!
+    //! @param pred
+    //! A function called as `pred(x)` for each element of the Functor,
+    //! and returning whether `f` should be applied on that element.
+    //!
+    //! @param f
+    //! A function called as `f(x)` on the element(s) of the Functor that
+    //! satisfy the predicate.
+    //!
+    //!
+    //! Example
+    //! -------
+    //! @include example/adjust_if.cpp
+#ifdef BOOST_HANA_DOXYGEN_INVOKED
+    constexpr auto adjust_if = [](auto&& xs, auto const& pred, auto const& f) {
+        return tag-dispatched;
+    };
+#else
+    template <typename Xs, typename = void>
+    struct adjust_if_impl : adjust_if_impl<Xs, when<true>> { };
+
+    struct adjust_if_t {
+        template <typename Xs, typename Pred, typename F>
+        constexpr auto operator()(Xs&& xs, Pred const& pred, F const& f) const;
+    };
+
+    constexpr adjust_if_t adjust_if{};
+#endif
+BOOST_HANA_NAMESPACE_END
+
+#endif // !BOOST_HANA_FWD_ADJUST_IF_HPP