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1 | /*! |
2 | @file | |
3 | Forward declares `boost::hana::unique`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
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_UNIQUE_HPP | |
11 | #define BOOST_HANA_FWD_UNIQUE_HPP | |
12 | ||
13 | #include <boost/hana/config.hpp> | |
14 | #include <boost/hana/core/when.hpp> | |
15 | #include <boost/hana/detail/nested_by_fwd.hpp> | |
16 | ||
17 | ||
18 | BOOST_HANA_NAMESPACE_BEGIN | |
19 | //! Removes all consecutive duplicate elements from a Sequence. | |
20 | //! @ingroup group-Sequence | |
21 | //! | |
22 | //! Given a `Sequence` and an optional binary predicate, `unique` returns | |
23 | //! a new sequence containing only the first element of every subrange | |
24 | //! of the original sequence whose elements are all equal. In other words, | |
25 | //! it turns a sequence of the form `[a, a, b, c, c, c, d, d, d, a]` into | |
26 | //! a sequence `[a, b, c, d, a]`. The equality of two elements is | |
27 | //! determined by the provided `predicate`, or by `equal` if no | |
28 | //! `predicate` is provided. | |
29 | //! | |
30 | //! | |
31 | //! Signature | |
32 | //! --------- | |
33 | //! Given a `Sequence` `S(T)`, a `Logical` `Bool` and a binary predicate | |
34 | //! \f$ T \times T \to Bool \f$, `unique` has the following signature: | |
35 | //! \f[ | |
36 | //! \mathtt{unique} : S(T) \times (T \times T \to Bool) \to S(T) | |
37 | //! \f] | |
38 | //! | |
39 | //! @param xs | |
40 | //! The sequence from which to remove consecutive duplicates. | |
41 | //! | |
42 | //! @param predicate | |
43 | //! A function called as `predicate(x, y)`, where `x` and `y` are adjacent | |
44 | //! elements of the sequence, and returning a `Logical` representing | |
45 | //! whether `x` and `y` should be considered equal. `predicate` should | |
46 | //! define an [equivalence relation][1] over the elements of the sequence. | |
47 | //! In the current implementation of the library, `predicate` has to | |
48 | //! return a compile-time `Logical`. This parameter is optional; it | |
49 | //! defaults to `equal` if it is not provided, which then requires the | |
50 | //! elements of the sequence to be compile-time `Comparable`. | |
51 | //! | |
52 | //! | |
53 | //! Syntactic sugar (`unique.by`) | |
54 | //! ----------------------------- | |
55 | //! `unique` can be called in an alternate way, which provides a nice | |
56 | //! syntax, especially in conjunction with the `comparing` combinator: | |
57 | //! @code | |
58 | //! unique.by(predicate, xs) == unique(xs, predicate) | |
59 | //! unique.by(predicate) == unique(-, predicate) | |
60 | //! @endcode | |
61 | //! | |
62 | //! where `unique(-, predicate)` denotes the partial application of | |
63 | //! `unique` to `predicate`. | |
64 | //! | |
65 | //! | |
66 | //! Example | |
67 | //! ------- | |
68 | //! @include example/unique.cpp | |
69 | //! | |
70 | //! [1]: http://en.wikipedia.org/wiki/Equivalence_relation#Definition | |
71 | #if defined(BOOST_HANA_DOXYGEN_INVOKED) | |
72 | constexpr auto unique = [](auto&& xs[, auto&& predicate]) { | |
73 | return tag-dispatched; | |
74 | }; | |
75 | #else | |
76 | template <typename S, typename = void> | |
77 | struct unique_impl : unique_impl<S, when<true>> { }; | |
78 | ||
79 | struct unique_t : detail::nested_by<unique_t> { | |
80 | template <typename Xs> | |
81 | constexpr auto operator()(Xs&& xs) const; | |
82 | ||
83 | template <typename Xs, typename Predicate> | |
84 | constexpr auto operator()(Xs&& xs, Predicate&& predicate) const; | |
85 | }; | |
86 | ||
87 | constexpr unique_t unique{}; | |
88 | #endif | |
89 | BOOST_HANA_NAMESPACE_END | |
90 | ||
91 | #endif // !BOOST_HANA_FWD_UNIQUE_HPP |