blob: 412614786d116020349011bec6c6bec910617519 (
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
|
/*!
@file
Forward declares `boost::hana::zero`.
@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_ZERO_HPP
#define BOOST_HANA_FWD_ZERO_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Identity of `plus`.
//! @ingroup group-Monoid
//!
//! @tparam M
//! The tag (a `Monoid`) of the returned identity.
//!
//!
//! Example
//! -------
//! @include example/zero.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
template <typename M>
constexpr auto zero = []() -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename M, typename = void>
struct zero_impl : zero_impl<M, when<true>> { };
template <typename M>
struct zero_t;
template <typename M>
constexpr zero_t<M> zero{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_ZERO_HPP
|