xref: /third_party/skia/include/private/SkTLogic.h (revision cb93a386) 
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#include "include/private/SkTo.h"
19
20namespace skstd {
21
22// C++17, <variant>
23struct monostate {};
24
25// C++17, <type_traits>
26template<typename...> struct conjunction : std::true_type { };
27template<typename T> struct conjunction<T> : T { };
28template<typename T, typename... Ts>
29struct conjunction<T, Ts...> : std::conditional<bool(T::value), conjunction<Ts...>, T>::type { };
30
31// C++17, std::data, std::size
32template<typename Container>
33constexpr auto data(Container& c) -> decltype(c.data()) { return c.data(); }
34template<typename Container>
35constexpr auto data(const Container& c) -> decltype(c.data()) { return c.data(); }
36template<typename Array, size_t N>
37constexpr auto data(Array(&a)[N]) -> decltype(a) { return a; }
38template<typename T>
39constexpr const T* data(std::initializer_list<T> i) { return i.begin(); }
40
41template<typename Container>
42constexpr auto size(Container& c) -> decltype(c.size()) { return c.size(); }
43template<typename Array, size_t N>
44constexpr size_t size(Array(&)[N]) { return N; }
45template<typename T>
46constexpr const T* size(std::initializer_list<T> i) { return i.end() - i.begin(); }
47}  // namespace skstd
48
49// The sknonstd namespace contains things we would like to be proposed and feel std-ish.
50namespace sknonstd {
51
52// The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'.
53// Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken).
54// std::experimental::propagate_const already exists for other purposes in TSv2.
55// These also follow the <dest, source> pattern used by boost.
56template <typename D, typename S> struct copy_const {
57    using type = std::conditional_t<std::is_const<S>::value, std::add_const_t<D>, D>;
58};
59template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type;
60
61template <typename D, typename S> struct copy_volatile {
62    using type = std::conditional_t<std::is_volatile<S>::value, std::add_volatile_t<D>, D>;
63};
64template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type;
65
66template <typename D, typename S> struct copy_cv {
67    using type = copy_volatile_t<copy_const_t<D, S>, S>;
68};
69template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type;
70
71// The name 'same' here means 'overwrite'.
72// Alternate proposed names are 'replace', 'transfer', or 'qualify_from'.
73// same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S>
74template <typename D, typename S> using same_const = copy_const<std::remove_const_t<D>, S>;
75template <typename D, typename S> using same_const_t = typename same_const<D, S>::type;
76template <typename D, typename S> using same_volatile =copy_volatile<std::remove_volatile_t<D>,S>;
77template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
78template <typename D, typename S> using same_cv = copy_cv<std::remove_cv_t<D>, S>;
79template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
80
81}  // namespace sknonstd
82
83template <typename Container>
84constexpr int SkCount(const Container& c) { return SkTo<int>(skstd::size(c)); }
85
86#endif
87