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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::lift`. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
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6 | Distributed 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_LIFT_HPP | |
11 | #define BOOST_HANA_FWD_LIFT_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | ||
16 | ||
1e59de90 | 17 | namespace boost { namespace hana { |
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18 | //! Lift a value into an `Applicative` structure. |
19 | //! @ingroup group-Applicative | |
20 | //! | |
21 | //! `lift<A>` takes a normal value and embeds it into a structure whose | |
22 | //! shape is represented by the `A` `Applicative`. Note that the value | |
23 | //! may be a function, in which case the created structure may be | |
24 | //! `ap`plied to another `Applicative` structure containing values. | |
25 | //! | |
26 | //! | |
27 | //! Signature | |
28 | //! --------- | |
29 | //! Given an Applicative `A`, the signature is | |
30 | //! @f$ \mathtt{lift}_A : T \to A(T) @f$. | |
31 | //! | |
32 | //! @tparam A | |
33 | //! A tag representing the `Applicative` into which the value is lifted. | |
34 | //! | |
35 | //! @param x | |
36 | //! The value to lift into the applicative. | |
37 | //! | |
38 | //! | |
39 | //! Example | |
40 | //! ------- | |
41 | //! @include example/lift.cpp | |
42 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
43 | template <typename A> | |
44 | constexpr auto lift = [](auto&& x) { | |
45 | return tag-dispatched; | |
46 | }; | |
47 | #else | |
48 | template <typename A, typename = void> | |
49 | struct lift_impl : lift_impl<A, when<true>> { }; | |
50 | ||
51 | template <typename A> | |
92f5a8d4 TL |
52 | struct lift_t { |
53 | template <typename X> | |
54 | constexpr auto operator()(X&& x) const; | |
55 | }; | |
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56 | |
57 | template <typename A> | |
1e59de90 | 58 | BOOST_HANA_INLINE_VARIABLE constexpr lift_t<A> lift{}; |
7c673cae | 59 | #endif |
1e59de90 | 60 | }} // end namespace boost::hana |
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61 | |
62 | #endif // !BOOST_HANA_FWD_LIFT_HPP |