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