projects / ceph.git / blame
| Commit | Line | Data |
|---|---|---|
| 7c673cae FG |
1 | /*! |
| 2 | @file | |
| 3 | Forward declares `boost::hana::equal`. | |
| 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_EQUAL_HPP | |
| 11 | #define BOOST_HANA_FWD_EQUAL_HPP | |
| 12 | ||
| 13 | #include <boost/hana/config.hpp> | |
| 14 | #include <boost/hana/core/when.hpp> | |
| 15 | #include <boost/hana/detail/nested_to_fwd.hpp> | |
| 16 | ||
| 17 | ||
| 18 | BOOST_HANA_NAMESPACE_BEGIN | |
| 19 | //! Returns a `Logical` representing whether `x` is equal to `y`. | |
| 20 | //! @ingroup group-Comparable | |
| 21 | //! | |
| 22 | //! The `equal` function can be called in two different ways. First, it | |
| 23 | //! can be called like a normal function: | |
| 24 | //! @code | |
| 25 | //! equal(x, y) | |
| 26 | //! @endcode | |
| 27 | //! | |
| 28 | //! However, it may also be partially applied to an argument by using | |
| 29 | //! `equal.to`: | |
| 30 | //! @code | |
| 31 | //! equal.to(x)(y) == equal(x, y) | |
| 32 | //! @endcode | |
| 33 | //! | |
| 34 | //! In other words, `equal.to(x)` is a function object that is equivalent | |
| 35 | //! to `partial(equal, x)`. This is provided to enhance the readability of | |
| 36 | //! some constructs, especially when using higher order algorithms. | |
| 37 | //! | |
| 38 | //! | |
| 39 | //! Signature | |
| 40 | //! --------- | |
| 41 | //! Given a Logical `Bool` and two Comparables `A` and `B` that | |
| 42 | //! share a common embedding, the signature is | |
| 43 | //! @f$ \mathtt{equal} : A \times B \to Bool @f$. | |
| 44 | //! | |
| 45 | //! @param x, y | |
| 46 | //! Two objects to compare for equality. | |
| 47 | //! | |
| 48 | //! | |
| 49 | //! Example | |
| 50 | //! ------- | |
| 51 | //! @include example/equal.cpp | |
| 52 | //! | |
| 53 | //! | |
| 54 | //! > #### Rationale for the arity of `equal` | |
| 55 | //! > It is a valid question whether `equal` should accept more than 2 | |
| 56 | //! > arguments and have semantics matching those of Python's `==`. This | |
| 57 | //! > is not supported right now for the following reasons: | |
| 58 | //! > - It was implemented in the MPL11, but it was not shown to be useful | |
| 59 | //! > so far. | |
| 60 | //! > - It does not make sense for `not_equal` to have an arity of more | |
| 61 | //! > than 2, only `equal` could maybe have those semantics, which would | |
| 62 | //! > break symmetry. | |
| 63 | #ifdef BOOST_HANA_DOXYGEN_INVOKED | |
| 64 | constexpr auto equal = [](auto&& x, auto&& y) { | |
| 65 | return tag-dispatched; | |
| 66 | }; | |
| 67 | #else | |
| 68 | template <typename T, typename U, typename = void> | |
| 69 | struct equal_impl : equal_impl<T, U, when<true>> { }; | |
| 70 | ||
| 71 | struct equal_t : detail::nested_to<equal_t> { | |
| 72 | template <typename X, typename Y> | |
| 73 | constexpr auto operator()(X&& x, Y&& y) const; | |
| 74 | }; | |
| 75 | ||
| 76 | constexpr equal_t equal{}; | |
| 77 | #endif | |
| 78 | BOOST_HANA_NAMESPACE_END | |
| 79 | ||
| 80 | #endif // !BOOST_HANA_FWD_EQUAL_HPP |