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1 | // -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- |
2 | // vim: ts=8 sw=2 smarttab | |
3 | /* | |
4 | * Ceph - scalable distributed file system | |
5 | * | |
6 | * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net> | |
7 | * | |
8 | * This is free software; you can redistribute it and/or | |
9 | * modify it under the terms of the GNU Lesser General Public | |
10 | * License version 2.1, as published by the Free Software | |
11 | * Foundation. See file COPYING. | |
12 | * | |
13 | */ | |
14 | ||
15 | #include <mutex> | |
16 | #include <memory> | |
17 | #include <optional> | |
18 | #include <shared_mutex> | |
19 | #include <type_traits> | |
20 | #include <utility> | |
21 | ||
22 | #include <boost/optional.hpp> | |
23 | ||
11fdf7f2 TL |
24 | #ifndef CEPH_COMMON_CONVENIENCE_H |
25 | #define CEPH_COMMON_CONVENIENCE_H | |
26 | ||
27 | namespace ceph { | |
28 | // boost::optional is wonderful! Unfortunately it lacks a function for | |
29 | // the thing you would most obviously want to do with it: apply a | |
30 | // function to its contents. | |
31 | ||
32 | // There are two obvious candidates. The first is a function that | |
33 | // takes a function and an optional value and returns an optional | |
34 | // value, either holding the return value of the function or holding | |
35 | // nothing. | |
36 | // | |
37 | // I'd considered making more overloads for mutable lvalue | |
38 | // references, but those are going a bit beyond likely use cases. | |
39 | // | |
40 | template<typename T, typename F> | |
41 | auto maybe_do(const boost::optional<T>& t, F&& f) -> | |
42 | boost::optional<std::result_of_t<F(const std::decay_t<T>)>> | |
43 | { | |
44 | if (t) | |
45 | return { std::forward<F>(f)(*t) }; | |
46 | else | |
47 | return boost::none; | |
48 | } | |
49 | ||
50 | // The other obvious function takes an optional but returns an | |
51 | // ‘unwrapped’ value, either the result of evaluating the function or | |
52 | // a provided alternate value. | |
53 | // | |
54 | template<typename T, typename F, typename U> | |
55 | auto maybe_do_or(const boost::optional<T>& t, F&& f, U&& u) -> | |
56 | std::result_of_t<F(const std::decay_t<T>)> | |
57 | { | |
58 | static_assert(std::is_convertible_v<U, std::result_of_t<F(T)>>, | |
59 | "Alternate value must be convertible to function return type."); | |
60 | if (t) | |
61 | return std::forward<F>(f)(*t); | |
62 | else | |
63 | return std::forward<U>(u); | |
64 | } | |
65 | ||
66 | ||
67 | // Same thing but for std::optional | |
68 | ||
69 | template<typename T, typename F> | |
70 | auto maybe_do(const std::optional<T>& t, F&& f) -> | |
71 | std::optional<std::result_of_t<F(const std::decay_t<T>)>> | |
72 | { | |
73 | if (t) | |
74 | return { std::forward<F>(f)(*t) }; | |
75 | else | |
76 | return std::nullopt; | |
77 | } | |
78 | ||
79 | // The other obvious function takes an optional but returns an | |
80 | // ‘unwrapped’ value, either the result of evaluating the function or | |
81 | // a provided alternate value. | |
82 | // | |
83 | template<typename T, typename F, typename U> | |
84 | auto maybe_do_or(const std::optional<T>& t, F&& f, U&& u) -> | |
85 | std::result_of_t<F(const std::decay_t<T>)> | |
86 | { | |
87 | static_assert(std::is_convertible_v<U, std::result_of_t<F(T)>>, | |
88 | "Alternate value must be convertible to function return type."); | |
89 | if (t) | |
90 | return std::forward<F>(f)(*t); | |
91 | else | |
92 | return std::forward<U>(u); | |
93 | } | |
94 | ||
95 | namespace _convenience { | |
96 | template<typename... Ts, typename F, std::size_t... Is> | |
97 | inline void for_each_helper(const std::tuple<Ts...>& t, const F& f, | |
98 | std::index_sequence<Is...>) { | |
99 | (f(std::get<Is>(t)), ..., void()); | |
100 | } | |
101 | template<typename... Ts, typename F, std::size_t... Is> | |
102 | inline void for_each_helper(std::tuple<Ts...>& t, const F& f, | |
103 | std::index_sequence<Is...>) { | |
104 | (f(std::get<Is>(t)), ..., void()); | |
105 | } | |
106 | template<typename... Ts, typename F, std::size_t... Is> | |
107 | inline void for_each_helper(const std::tuple<Ts...>& t, F& f, | |
108 | std::index_sequence<Is...>) { | |
109 | (f(std::get<Is>(t)), ..., void()); | |
110 | } | |
111 | template<typename... Ts, typename F, std::size_t... Is> | |
112 | inline void for_each_helper(std::tuple<Ts...>& t, F& f, | |
113 | std::index_sequence<Is...>) { | |
114 | (f(std::get<Is>(t)), ..., void()); | |
115 | } | |
116 | } | |
117 | ||
118 | template<typename... Ts, typename F> | |
119 | inline void for_each(const std::tuple<Ts...>& t, const F& f) { | |
120 | _convenience::for_each_helper(t, f, std::index_sequence_for<Ts...>{}); | |
121 | } | |
122 | template<typename... Ts, typename F> | |
123 | inline void for_each(std::tuple<Ts...>& t, const F& f) { | |
124 | _convenience::for_each_helper(t, f, std::index_sequence_for<Ts...>{}); | |
125 | } | |
126 | template<typename... Ts, typename F> | |
127 | inline void for_each(const std::tuple<Ts...>& t, F& f) { | |
128 | _convenience::for_each_helper(t, f, std::index_sequence_for<Ts...>{}); | |
129 | } | |
130 | template<typename... Ts, typename F> | |
131 | inline void for_each(std::tuple<Ts...>& t, F& f) { | |
132 | _convenience::for_each_helper(t, f, std::index_sequence_for<Ts...>{}); | |
133 | } | |
134 | } | |
135 | #endif // CEPH_COMMON_CONVENIENCE_H |