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author | DongHun Kwak <dh0128.kwak@samsung.com> | 2016-10-06 10:38:45 +0900 |
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committer | DongHun Kwak <dh0128.kwak@samsung.com> | 2016-10-06 10:39:52 +0900 |
commit | 5cde13f21d36c7224b0e13d11c4b49379ae5210d (patch) | |
tree | e8269ac85a4b0f7d416e2565fa4f451b5cb41351 /boost/hana/fwd/at_key.hpp | |
parent | d9ec475d945d3035377a0d89ed42e382d8988891 (diff) | |
download | boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.tar.gz boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.tar.bz2 boost-5cde13f21d36c7224b0e13d11c4b49379ae5210d.zip |
Imported Upstream version 1.61.0
Change-Id: I96a1f878d1e6164f01e9aadd5147f38fca448d90
Signed-off-by: DongHun Kwak <dh0128.kwak@samsung.com>
Diffstat (limited to 'boost/hana/fwd/at_key.hpp')
-rw-r--r-- | boost/hana/fwd/at_key.hpp | 75 |
1 files changed, 75 insertions, 0 deletions
diff --git a/boost/hana/fwd/at_key.hpp b/boost/hana/fwd/at_key.hpp new file mode 100644 index 0000000000..a3045bba0e --- /dev/null +++ b/boost/hana/fwd/at_key.hpp @@ -0,0 +1,75 @@ +/*! +@file +Forward declares `boost::hana::at_key`. + +@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_AT_KEY_HPP +#define BOOST_HANA_FWD_AT_KEY_HPP + +#include <boost/hana/config.hpp> +#include <boost/hana/core/when.hpp> + + +BOOST_HANA_NAMESPACE_BEGIN + //! Returns the value associated to the given key in a structure, or fail. + //! @ingroup group-Searchable + //! + //! Given a `key` and a `Searchable` structure, `at_key` returns the first + //! value whose key is equal to the given `key`, and fails at compile-time + //! if no such key exists. This requires the `key` to be compile-time + //! `Comparable`, exactly like for `find`. `at_key` satisfies the following: + //! @code + //! at_key(xs, key) == find(xs, key).value() + //! @endcode + //! + //! If the `Searchable` actually stores the elements it contains, `at_key` + //! is required to return a lvalue reference, a lvalue reference to const + //! or a rvalue reference to the found value, where the type of reference + //! must match that of the structure passed to `at_key`. If the `Searchable` + //! does not store the elements it contains (i.e. it generates them on + //! demand), this requirement is dropped. + //! + //! + //! @param xs + //! The structure to be searched. + //! + //! @param key + //! A key to be searched for in the structure. The key has to be + //! `Comparable` with the other keys of the structure. In the current + //! version of the library, the comparison of `key` with any other key + //! of the structure must return a compile-time `Logical`. + //! + //! + //! Example + //! ------- + //! @include example/at_key.cpp + //! + //! + //! Benchmarks + //! ---------- + //! <div class="benchmark-chart" + //! style="min-width: 310px; height: 400px; margin: 0 auto" + //! data-dataset="benchmark.at_key.number_of_lookups.chart.json"> + //! </div> +#ifdef BOOST_HANA_DOXYGEN_INVOKED + constexpr auto at_key = [](auto&& xs, auto const& key) -> decltype(auto) { + return tag-dispatched; + }; +#else + template <typename S, typename = void> + struct at_key_impl : at_key_impl<S, when<true>> { }; + + struct at_key_t { + template <typename Xs, typename Key> + constexpr decltype(auto) operator()(Xs&& xs, Key const& key) const; + }; + + constexpr at_key_t at_key{}; +#endif +BOOST_HANA_NAMESPACE_END + +#endif // !BOOST_HANA_FWD_AT_KEY_HPP |