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 <new> // see bug 981264 19 #include <type_traits> 20 21 namespace skstd { 22 23 template <bool B> using bool_constant = std::integral_constant<bool, B>; 24 25 template <bool B, typename T, typename F> using conditional_t = typename std::conditional<B, T, F>::type; 26 template <bool B, typename T = void> using enable_if_t = typename std::enable_if<B, T>::type; 27 28 template <typename T> using remove_const_t = typename std::remove_const<T>::type; 29 template <typename T> using remove_volatile_t = typename std::remove_volatile<T>::type; 30 template <typename T> using remove_cv_t = typename std::remove_cv<T>::type; 31 template <typename T> using remove_pointer_t = typename std::remove_pointer<T>::type; 32 template <typename T> using remove_reference_t = typename std::remove_reference<T>::type; 33 template <typename T> using remove_extent_t = typename std::remove_extent<T>::type; 34 35 template <typename T> using add_const_t = typename std::add_const<T>::type; 36 template <typename T> using add_volatile_t = typename std::add_volatile<T>::type; 37 template <typename T> using add_cv_t = typename std::add_cv<T>::type; 38 template <typename T> using add_pointer_t = typename std::add_pointer<T>::type; 39 template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type; 40 41 template <typename T> using result_of_t = typename std::result_of<T>::type; 42 43 template <typename... T> using common_type_t = typename std::common_type<T...>::type; 44 45 template <std::size_t... Ints> struct index_sequence { 46 using type = index_sequence; 47 using value_type = std::size_t; sizeindex_sequence48 static constexpr std::size_t size() noexcept { return sizeof...(Ints); } 49 }; 50 51 template <typename S1, typename S2> struct make_index_sequence_combine; 52 template <std::size_t... I1, std::size_t... I2> 53 struct make_index_sequence_combine<skstd::index_sequence<I1...>, skstd::index_sequence<I2...>> 54 : skstd::index_sequence<I1..., (sizeof...(I1)+I2)...> 55 { }; 56 57 template <std::size_t N> struct make_index_sequence 58 : make_index_sequence_combine<typename skstd::make_index_sequence< N/2>::type, 59 typename skstd::make_index_sequence<N - N/2>::type>{}; 60 template<> struct make_index_sequence<0> : skstd::index_sequence< >{}; 61 template<> struct make_index_sequence<1> : skstd::index_sequence<0>{}; 62 63 struct monostate {}; 64 65 template<typename...> struct conjunction : std::true_type { }; 66 template<typename B0> struct conjunction<B0> : B0 { }; 67 template<typename B0, typename... Bs> 68 struct conjunction<B0, Bs...> : std::conditional<bool(B0::value), conjunction<Bs...>, B0>::type { }; 69 } // namespace skstd 70 71 // The sknonstd namespace contains things we would like to be proposed and feel std-ish. 72 namespace sknonstd { 73 74 // The name 'copy' here is fraught with peril. In this case it means 'append', not 'overwrite'. 75 // Alternate proposed names are 'propagate', 'augment', or 'append' (and 'add', but already taken). 76 // std::experimental::propagate_const already exists for other purposes in TSv2. 77 // These also follow the <dest, source> pattern used by boost. 78 template <typename D, typename S> struct copy_const { 79 using type = skstd::conditional_t<std::is_const<S>::value, skstd::add_const_t<D>, D>; 80 }; 81 template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type; 82 83 template <typename D, typename S> struct copy_volatile { 84 using type = skstd::conditional_t<std::is_volatile<S>::value, skstd::add_volatile_t<D>, D>; 85 }; 86 template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type; 87 88 template <typename D, typename S> struct copy_cv { 89 using type = copy_volatile_t<copy_const_t<D, S>, S>; 90 }; 91 template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type; 92 93 // The name 'same' here means 'overwrite'. 94 // Alternate proposed names are 'replace', 'transfer', or 'qualify_from'. 95 // same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S> 96 template <typename D, typename S> using same_const = copy_const<skstd::remove_const_t<D>, S>; 97 template <typename D, typename S> using same_const_t = typename same_const<D, S>::type; 98 template <typename D, typename S> using same_volatile =copy_volatile<skstd::remove_volatile_t<D>,S>; 99 template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type; 100 template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>; 101 template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type; 102 103 } // namespace sknonstd 104 105 // Just a pithier wrapper for enable_if_t. 106 #define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T> 107 108 #endif 109