blob: 8356cddeabfad2eff9b9a50311aca9aa950d3d9e (
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
47
48
|
/*!
@file
Forward declares `boost::hana::back`.
@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_BACK_HPP
#define BOOST_HANA_FWD_BACK_HPP
#include <boost/hana/config.hpp>
#include <boost/hana/core/when.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! Returns the last element of a non-empty and finite iterable.
//! @ingroup group-Iterable
//!
//! Given a non-empty and finite iterable `xs` with a linearization of
//! `[x1, ..., xN]`, `back(xs)` is equal to `xN`. Equivalently, `back(xs)`
//! must be equivalent to `at_c<N-1>(xs)`, and that regardless of the
//! value category of `xs` (`back` must respect the reference semantics
//! of `at`).
//!
//!
//! Example
//! -------
//! @include example/back.cpp
#ifdef BOOST_HANA_DOXYGEN_INVOKED
constexpr auto back = [](auto&& xs) -> decltype(auto) {
return tag-dispatched;
};
#else
template <typename It, typename = void>
struct back_impl : back_impl<It, when<true>> { };
struct back_t {
template <typename Xs>
constexpr decltype(auto) operator()(Xs&& xs) const;
};
constexpr back_t back{};
#endif
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_FWD_BACK_HPP
|
