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 <array> 18 #include <stddef.h> 19 #include <stdint.h> 20 #include <type_traits> 21 #include <utility> 22 23 namespace skstd { 24 25 template <bool B> using bool_constant = std::integral_constant<bool, B>; 26 27 template <bool B, typename T, typename F> using conditional_t = typename std::conditional<B, T, F>::type; 28 template <bool B, typename T = void> using enable_if_t = typename std::enable_if<B, T>::type; 29 30 template <typename T> using remove_const_t = typename std::remove_const<T>::type; 31 template <typename T> using remove_volatile_t = typename std::remove_volatile<T>::type; 32 template <typename T> using remove_cv_t = typename std::remove_cv<T>::type; 33 template <typename T> using remove_pointer_t = typename std::remove_pointer<T>::type; 34 template <typename T> using remove_reference_t = typename std::remove_reference<T>::type; 35 template <typename T> using remove_extent_t = typename std::remove_extent<T>::type; 36 37 template <typename T> using add_const_t = typename std::add_const<T>::type; 38 template <typename T> using add_volatile_t = typename std::add_volatile<T>::type; 39 template <typename T> using add_cv_t = typename std::add_cv<T>::type; 40 template <typename T> using add_pointer_t = typename std::add_pointer<T>::type; 41 template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type; 42 43 template <typename T> using result_of_t = typename std::result_of<T>::type; 44 45 template <typename... T> using common_type_t = typename std::common_type<T...>::type; 46 47 // Chromium currently requires gcc 4.8.2 or a recent clang compiler, but uses libstdc++4.6.4. 48 // Note that Precise actually uses libstdc++4.6.3. 49 // Unfortunately, libstdc++ STL before libstdc++4.7 do not define std::underlying_type. 50 // Newer gcc and clang compilers have __underlying_type which does not depend on runtime support. 51 // See https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html for __GLIBCXX__ values. 52 // Unfortunately __GLIBCXX__ is a date, but no updates to versions before 4.7 are now anticipated. 53 #define SK_GLIBCXX_4_7_0 20120322 54 // Updates to versions before 4.7 but released after 4.7 was released. 55 #define SK_GLIBCXX_4_5_4 20120702 56 #define SK_GLIBCXX_4_6_4 20121127 57 #if defined(__GLIBCXX__) && (__GLIBCXX__ < SK_GLIBCXX_4_7_0 || \ 58 __GLIBCXX__ == SK_GLIBCXX_4_5_4 || \ 59 __GLIBCXX__ == SK_GLIBCXX_4_6_4) 60 template <typename T> struct underlying_type { 61 using type = __underlying_type(T); 62 }; 63 template <typename T> using is_trivially_destructible = std::has_trivial_destructor<T>; 64 #else 65 template <typename T> using underlying_type = std::underlying_type<T>; 66 template <typename T> using is_trivially_destructible = std::is_trivially_destructible<T>; 67 #endif 68 template <typename T> using underlying_type_t = typename skstd::underlying_type<T>::type; 69 70 71 template <std::size_t... Ints> struct index_sequence { 72 using type = index_sequence; 73 using value_type = size_t; 74 static constexpr std::size_t size() noexcept { return sizeof...(Ints); } 75 }; 76 77 template <typename S1, typename S2> struct make_index_sequence_combine; 78 template <size_t... I1, size_t... I2> 79 struct make_index_sequence_combine<skstd::index_sequence<I1...>, skstd::index_sequence<I2...>> 80 : skstd::index_sequence<I1..., (sizeof...(I1)+I2)...> 81 { }; 82 83 template <size_t N> struct make_index_sequence 84 : make_index_sequence_combine<typename skstd::make_index_sequence< N/2>::type, 85 typename skstd::make_index_sequence<N - N/2>::type>{}; 86 template<> struct make_index_sequence<0> : skstd::index_sequence< >{}; 87 template<> struct make_index_sequence<1> : skstd::index_sequence<0>{}; 88 89 } // namespace skstd 90 91 // The sknonstd namespace contains things we would like to be proposed and feel std-ish. 92 namespace sknonstd { 93 94 // The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'. 95 // Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken). 96 // std::experimental::propagate_const already exists for other purposes in TSv2. 97 // These also follow the <dest, source> pattern used by boost. 98 template <typename D, typename S> struct copy_const { 99 using type = skstd::conditional_t<std::is_const<S>::value, skstd::add_const_t<D>, D>; 100 }; 101 template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type; 102 103 template <typename D, typename S> struct copy_volatile { 104 using type = skstd::conditional_t<std::is_volatile<S>::value, skstd::add_volatile_t<D>, D>; 105 }; 106 template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type; 107 108 template <typename D, typename S> struct copy_cv { 109 using type = copy_volatile_t<copy_const_t<D, S>, S>; 110 }; 111 template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type; 112 113 // The name 'same' here means 'overwrite'. 114 // Alternate proposed names are 'replace', 'transfer', or 'qualify_from'. 115 // same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S> 116 template <typename D, typename S> using same_const = copy_const<skstd::remove_const_t<D>, S>; 117 template <typename D, typename S> using same_const_t = typename same_const<D, S>::type; 118 template <typename D, typename S> using same_volatile =copy_volatile<skstd::remove_volatile_t<D>,S>; 119 template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type; 120 template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>; 121 template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type; 122 123 } // namespace sknonstd 124 125 // Just a pithier wrapper for enable_if_t. 126 #define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T> 127 128 #endif 129