blob: d0d2da94a911a9bce5511cfa2cde2bd17a405870 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
|
/*!
@file
Forward declares `boost::hana::none`.
@copyright Louis Dionne 2013-2017
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_NONE_HPP
#define BOOST_HANA_FWD_NONE_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Returns whether all of the keys of the structure are false-valued.
//! @ingroup group-Searchable
//!
//! The keys of the structure must be `Logical`s. If the structure is not
//! finite, a true-valued key must appear at a finite "index" in order
//! for this method to finish.
//!
//!
//! Example
//! -------
//! @include example/none.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto none = [](auto&& xs) -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename S, typename = void>
struct none_impl : none_impl<S, when<true>> { };
struct none_t {
template <typename Xs>
constexpr auto operator()(Xs&& xs) const;
};
constexpr none_t none{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_NONE_HPP
|
