1/*
2 * Copyright 2013 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 *
7 *
8 * This header provides some std:: features early in the skstd namespace
9 * and several Skia-specific additions in the sknonstd namespace.
10 */
11
12#ifndef SkTLogic_DEFINED
13#define SkTLogic_DEFINED
14
15#include <cstddef>
16#include <type_traits>
17#include <utility>
18
19namespace skstd {
20
21// C++17, <variant>
22struct monostate {};
23
24// C++17, <type_traits>
25template<typename...> struct conjunction : std::true_type { };
26template<typename T> struct conjunction<T> : T { };
27template<typename T, typename... Ts>
28struct conjunction<T, Ts...> : std::conditional<bool(T::value), conjunction<Ts...>, T>::type { };
29
30} // namespace skstd
31
32// The sknonstd namespace contains things we would like to be proposed and feel std-ish.
33namespace sknonstd {
34
35// The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'.
36// Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken).
37// std::experimental::propagate_const already exists for other purposes in TSv2.
38// These also follow the <dest, source> pattern used by boost.
39template <typename D, typename S> struct copy_const {
40 using type = std::conditional_t<std::is_const<S>::value, std::add_const_t<D>, D>;
41};
42template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type;
43
44template <typename D, typename S> struct copy_volatile {
45 using type = std::conditional_t<std::is_volatile<S>::value, std::add_volatile_t<D>, D>;
46};
47template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type;
48
49template <typename D, typename S> struct copy_cv {
50 using type = copy_volatile_t<copy_const_t<D, S>, S>;
51};
52template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type;
53
54// The name 'same' here means 'overwrite'.
55// Alternate proposed names are 'replace', 'transfer', or 'qualify_from'.
56// same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S>
57template <typename D, typename S> using same_const = copy_const<std::remove_const_t<D>, S>;
58template <typename D, typename S> using same_const_t = typename same_const<D, S>::type;
59template <typename D, typename S> using same_volatile =copy_volatile<std::remove_volatile_t<D>,S>;
60template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
61template <typename D, typename S> using same_cv = copy_cv<std::remove_cv_t<D>, S>;
62template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
63
64} // namespace sknonstd
65
66#endif
67