internal/span.h
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1 //
2 // Copyright 2019 The Abseil Authors.
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 // https://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 //
16 #ifndef ABSL_TYPES_INTERNAL_SPAN_H_
17 #define ABSL_TYPES_INTERNAL_SPAN_H_
18 
19 #include <algorithm>
20 #include <cstddef>
21 #include <string>
22 #include <type_traits>
23 
26 #include "absl/meta/type_traits.h"
27 
28 namespace absl {
29 
30 namespace span_internal {
31 // A constexpr min function
32 constexpr size_t Min(size_t a, size_t b) noexcept { return a < b ? a : b; }
33 
34 // Wrappers for access to container data pointers.
35 template <typename C>
36 constexpr auto GetDataImpl(C& c, char) noexcept // NOLINT(runtime/references)
37  -> decltype(c.data()) {
38  return c.data();
39 }
40 
41 // Before C++17, std::string::data returns a const char* in all cases.
42 inline char* GetDataImpl(std::string& s, // NOLINT(runtime/references)
43  int) noexcept {
44  return &s[0];
45 }
46 
47 template <typename C>
48 constexpr auto GetData(C& c) noexcept // NOLINT(runtime/references)
49  -> decltype(GetDataImpl(c, 0)) {
50  return GetDataImpl(c, 0);
51 }
52 
53 // Detection idioms for size() and data().
54 template <typename C>
55 using HasSize =
56  std::is_integral<absl::decay_t<decltype(std::declval<C&>().size())>>;
57 
58 // We want to enable conversion from vector<T*> to Span<const T* const> but
59 // disable conversion from vector<Derived> to Span<Base>. Here we use
60 // the fact that U** is convertible to Q* const* if and only if Q is the same
61 // type or a more cv-qualified version of U. We also decay the result type of
62 // data() to avoid problems with classes which have a member function data()
63 // which returns a reference.
64 template <typename T, typename C>
65 using HasData =
66  std::is_convertible<absl::decay_t<decltype(GetData(std::declval<C&>()))>*,
67  T* const*>;
68 
69 // Extracts value type from a Container
70 template <typename C>
71 struct ElementType {
73 };
74 
75 template <typename T, size_t N>
76 struct ElementType<T (&)[N]> {
77  using type = T;
78 };
79 
80 template <typename C>
81 using ElementT = typename ElementType<C>::type;
82 
83 template <typename T>
84 using EnableIfMutable =
86 
87 template <template <typename> class SpanT, typename T>
88 bool EqualImpl(SpanT<T> a, SpanT<T> b) {
89  static_assert(std::is_const<T>::value, "");
90  return absl::equal(a.begin(), a.end(), b.begin(), b.end());
91 }
92 
93 template <template <typename> class SpanT, typename T>
94 bool LessThanImpl(SpanT<T> a, SpanT<T> b) {
95  // We can't use value_type since that is remove_cv_t<T>, so we go the long way
96  // around.
97  static_assert(std::is_const<T>::value, "");
98  return std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end());
99 }
100 
101 // The `IsConvertible` classes here are needed because of the
102 // `std::is_convertible` bug in libcxx when compiled with GCC. This build
103 // configuration is used by Android NDK toolchain. Reference link:
104 // https://bugs.llvm.org/show_bug.cgi?id=27538.
105 template <typename From, typename To>
107  private:
108  static std::true_type testval(To);
109  static std::false_type testval(...);
110 
111  public:
112  using type = decltype(testval(std::declval<From>()));
113 };
114 
115 template <typename From, typename To>
116 struct IsConvertible : IsConvertibleHelper<From, To>::type {};
117 
118 // TODO(zhangxy): replace `IsConvertible` with `std::is_convertible` once the
119 // older version of libcxx is not supported.
120 template <typename From, typename To>
121 using EnableIfConvertibleTo =
123 } // namespace span_internal
124 } // namespace absl
125 
126 #endif // ABSL_TYPES_INTERNAL_SPAN_H_
typename absl::remove_reference_t< C >::value_type type
Definition: internal/span.h:72
std::is_integral< absl::decay_t< decltype(std::declval< C & >().size())>> HasSize
Definition: internal/span.h:56
bool EqualImpl(SpanT< T > a, SpanT< T > b)
Definition: internal/span.h:88
typename std::remove_reference< T >::type remove_reference_t
Definition: type_traits.h:513
decltype(testval(std::declval< From >())) type
constexpr auto GetData(C &c) noexcept-> decltype(GetDataImpl(c, 0))
Definition: internal/span.h:48
Definition: algorithm.h:29
constexpr size_t Min(size_t a, size_t b) noexcept
Definition: internal/span.h:32
typename std::enable_if< IsConvertible< From, To >::value >::type EnableIfConvertibleTo
size_t value
static char data[kDataSize]
Definition: city_test.cc:31
std::is_convertible< absl::decay_t< decltype(GetData(std::declval< C & >()))> *, T *const * > HasData
Definition: internal/span.h:67
bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2, InputIter2 last2, Pred &&pred)
Definition: algorithm.h:99
typename std::enable_if<!std::is_const< T >::value, int >::type EnableIfMutable
Definition: internal/span.h:85
uintptr_t size
constexpr auto GetDataImpl(C &c, char) noexcept-> decltype(c.data())
Definition: internal/span.h:36
uint64_t b
Definition: layout_test.cc:50
bool LessThanImpl(SpanT< T > a, SpanT< T > b)
Definition: internal/span.h:94
typename ElementType< C >::type ElementT
Definition: internal/span.h:81


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autogenerated on Tue Jun 18 2019 19:44:37