SkTLogic.h 4.7 KB

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  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. #ifndef SkTLogic_DEFINED
  14. #define SkTLogic_DEFINED
  15. #include <cstddef>
  16. #include <type_traits>
  17. namespace skstd {
  18. template <bool B> using bool_constant = std::integral_constant<bool, B>;
  19. template <bool B, typename T, typename F> using conditional_t = typename std::conditional<B, T, F>::type;
  20. template <bool B, typename T = void> using enable_if_t = typename std::enable_if<B, T>::type;
  21. template <typename T> using remove_const_t = typename std::remove_const<T>::type;
  22. template <typename T> using remove_volatile_t = typename std::remove_volatile<T>::type;
  23. template <typename T> using remove_cv_t = typename std::remove_cv<T>::type;
  24. template <typename T> using remove_pointer_t = typename std::remove_pointer<T>::type;
  25. template <typename T> using remove_reference_t = typename std::remove_reference<T>::type;
  26. template <typename T> using remove_extent_t = typename std::remove_extent<T>::type;
  27. template <typename T> using add_const_t = typename std::add_const<T>::type;
  28. template <typename T> using add_volatile_t = typename std::add_volatile<T>::type;
  29. template <typename T> using add_cv_t = typename std::add_cv<T>::type;
  30. template <typename T> using add_pointer_t = typename std::add_pointer<T>::type;
  31. template <typename T> using add_lvalue_reference_t = typename std::add_lvalue_reference<T>::type;
  32. template <typename T> using result_of_t = typename std::result_of<T>::type;
  33. template <typename... T> using common_type_t = typename std::common_type<T...>::type;
  34. template <std::size_t... Ints> struct index_sequence {
  35. using type = index_sequence;
  36. using value_type = std::size_t;
  37. static constexpr std::size_t size() noexcept { return sizeof...(Ints); }
  38. };
  39. template <typename S1, typename S2> struct make_index_sequence_combine;
  40. template <std::size_t... I1, std::size_t... I2>
  41. struct make_index_sequence_combine<skstd::index_sequence<I1...>, skstd::index_sequence<I2...>>
  42. : skstd::index_sequence<I1..., (sizeof...(I1)+I2)...>
  43. { };
  44. template <std::size_t N> struct make_index_sequence
  45. : make_index_sequence_combine<typename skstd::make_index_sequence< N/2>::type,
  46. typename skstd::make_index_sequence<N - N/2>::type>{};
  47. template<> struct make_index_sequence<0> : skstd::index_sequence< >{};
  48. template<> struct make_index_sequence<1> : skstd::index_sequence<0>{};
  49. } // namespace skstd
  50. // The sknonstd namespace contains things we would like to be proposed and feel std-ish.
  51. namespace sknonstd {
  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.
  56. template <typename D, typename S> struct copy_const {
  57. using type = skstd::conditional_t<std::is_const<S>::value, skstd::add_const_t<D>, D>;
  58. };
  59. template <typename D, typename S> using copy_const_t = typename copy_const<D, S>::type;
  60. template <typename D, typename S> struct copy_volatile {
  61. using type = skstd::conditional_t<std::is_volatile<S>::value, skstd::add_volatile_t<D>, D>;
  62. };
  63. template <typename D, typename S> using copy_volatile_t = typename copy_volatile<D, S>::type;
  64. template <typename D, typename S> struct copy_cv {
  65. using type = copy_volatile_t<copy_const_t<D, S>, S>;
  66. };
  67. template <typename D, typename S> using copy_cv_t = typename copy_cv<D, S>::type;
  68. // The name 'same' here means 'overwrite'.
  69. // Alternate proposed names are 'replace', 'transfer', or 'qualify_from'.
  70. // same_xxx<D, S> can be written as copy_xxx<remove_xxx_t<D>, S>
  71. template <typename D, typename S> using same_const = copy_const<skstd::remove_const_t<D>, S>;
  72. template <typename D, typename S> using same_const_t = typename same_const<D, S>::type;
  73. template <typename D, typename S> using same_volatile =copy_volatile<skstd::remove_volatile_t<D>,S>;
  74. template <typename D, typename S> using same_volatile_t = typename same_volatile<D, S>::type;
  75. template <typename D, typename S> using same_cv = copy_cv<skstd::remove_cv_t<D>, S>;
  76. template <typename D, typename S> using same_cv_t = typename same_cv<D, S>::type;
  77. } // namespace sknonstd
  78. // Just a pithier wrapper for enable_if_t.
  79. #define SK_WHEN(condition, T) skstd::enable_if_t<!!(condition), T>
  80. #endif