1/*!
2@file
3Forward declares `boost::hana::extend`.
4
5Copyright Louis Dionne 2013-2022
6Distributed under the Boost Software License, Version 1.0.
7(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
8 */
9
10#ifndef BOOST_HANA_FWD_EXTEND_HPP
11#define BOOST_HANA_FWD_EXTEND_HPP
12
13#include <boost/hana/config.hpp>
14#include <boost/hana/core/when.hpp>
15
16
17namespace boost { namespace hana {
18 //! Comonadic application of a function to a comonadic value.
19 //! @ingroup group-Comonad
20 //!
21 //! Given a comonadic value and a function accepting a comonadic input,
22 //! `extend` returns the result of applying the function to that input
23 //! inside the comonadic context.
24 //!
25 //!
26 //! Signature
27 //! ---------
28 //! Given a Comonad `W` and a function of type \f$ W(T) \to U \f$, the
29 //! signature is
30 //! \f$
31 //! \mathtt{extend} : W(T) \times (W(T) \to U) \to W(U)
32 //! \f$
33 //!
34 //! @param w
35 //! A comonadic value to call the function with.
36 //!
37 //! @param f
38 //! A function of signature \f$ W(T) \to U \f$ to be applied to its
39 //! comonadic argument inside the comonadic context.
40 //!
41 //!
42 //! Example
43 //! -------
44 //! @include example/extend.cpp
45#ifdef BOOST_HANA_DOXYGEN_INVOKED
46 constexpr auto extend = [](auto&& w, auto&& f) -> decltype(auto) {
47 return tag-dispatched;
48 };
49#else
50 template <typename W, typename = void>
51 struct extend_impl : extend_impl<W, when<true>> { };
52
53 struct extend_t {
54 template <typename W_, typename F>
55 constexpr decltype(auto) operator()(W_&& w, F&& f) const;
56 };
57
58 BOOST_HANA_INLINE_VARIABLE constexpr extend_t extend{};
59#endif
60}} // end namespace boost::hana
61
62#endif // !BOOST_HANA_FWD_EXTEND_HPP
63

source code of boost/libs/hana/include/boost/hana/fwd/extend.hpp