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 of the helpers (like std::enable_if_t) which will
9 * become available with C++14 in the type_traits header (in the skstd
10 * namespace). This header also provides several Skia specific additions such
11 * as SK_WHEN and the sknonstd namespace.
12 */
13
14#ifndef SkTLogic_DEFINED
15#define SkTLogic_DEFINED
16
17#include <cstddef>
18#include <type_traits>
19
20namespace skstd {
21
22template <bool B> using bool_constant = std::integral_constant<bool, B>;
23
24template <bool B, typename T, typename F> using conditional_t = typename std::conditional<B, T, F>::type;
25template <bool B, typename T = void> using enable_if_t = typename std::enable_if<B, T>::type;
26
27template <typename T> using remove_const_t = typename std::remove_const<T>::type;
28template <typename T> using remove_volatile_t = typename std::remove_volatile<T>::type;
29template <typename T> using remove_cv_t = typename std::remove_cv<T>::type;
30template <typename T> using remove_pointer_t = typename std::remove_pointer<T>::type;
31template <typename T> using remove_reference_t = typename std::remove_reference<T>::type;
32template <typename T> using remove_extent_t = typename std::remove_extent<T>::type;
33
34template <typename T> using add_const_t = typename std::add_const<T>::type;
35template <typename T> using add_volatile_t = typename std::add_volatile<T>::type;
36template <typename T> using add_cv_t = typename std::add_cv<T>::type;
37template <typename T> using add_pointer_t = typename std::add_pointer<T>::type;
38template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
39
40template <typename T> using result_of_t = typename std::result_of<T>::type;
41
42template <typename... T> using common_type_t = typename std::common_type<T...>::type;
43
44template <std::size_t... Ints> struct index_sequence {
45 using type = index_sequence;
46 using value_type = std::size_t;
47 static constexpr std::size_t size() noexcept { return sizeof...(Ints); }
48};
49
50template <typename S1, typename S2> struct make_index_sequence_combine;
51template <std::size_t... I1, std::size_t... I2>
52struct make_index_sequence_combine<skstd::index_sequence<I1...>, skstd::index_sequence<I2...>>
53 : skstd::index_sequence<I1..., (sizeof...(I1)+I2)...>
54{ };
55
56template <std::size_t N> struct make_index_sequence
57 : make_index_sequence_combine<typename skstd::make_index_sequence< N/2>::type,
58 typename skstd::make_index_sequence<N - N/2>::type>{};
59template<> struct make_index_sequence<0> : skstd::index_sequence< >{};
60template<> struct make_index_sequence<1> : skstd::index_sequence<0>{};
61
62struct monostate {};
63
64template<typename...> struct conjunction : std::true_type { };
65template<typename T> struct conjunction<T> : T { };
66template<typename T, typename... Ts>
67struct conjunction<T, Ts...> : std::conditional<bool(T::value), conjunction<Ts...>, T>::type { };
68} // namespace skstd
69
70// The sknonstd namespace contains things we would like to be proposed and feel std-ish.
71namespace sknonstd {
72
73// The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'.
74// Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken).
75// std::experimental::propagate_const already exists for other purposes in TSv2.
76// These also follow the <dest, source> pattern used by boost.
77template <typename D, typename S> struct copy_const {
78 using type = skstd::conditional_t<std::is_const<S>::value, skstd::add_const_t<D>, D>;
79};
80template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type;
81
82template <typename D, typename S> struct copy_volatile {
83 using type = skstd::conditional_t<std::is_volatile<S>::value, skstd::add_volatile_t<D>, D>;
84};
85template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type;
86
87template <typename D, typename S> struct copy_cv {
88 using type = copy_volatile_t<copy_const_t<D, S>, S>;
89};
90template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type;
91
92// The name 'same' here means 'overwrite'.
93// Alternate proposed names are 'replace', 'transfer', or 'qualify_from'.
94// same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S>
95template <typename D, typename S> using same_const = copy_const<skstd::remove_const_t<D>, S>;
96template <typename D, typename S> using same_const_t = typename same_const<D, S>::type;
97template <typename D, typename S> using same_volatile =copy_volatile<skstd::remove_volatile_t<D>,S>;
98template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
99template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>;
100template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
101
102} // namespace sknonstd
103
104// Just a pithier wrapper for enable_if_t.
105#define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T>
106
107#endif
108