src/gromacs/utility/enumerationhelpers.h

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  35 /*! \file
  36  * \brief Defines helper types for class enumerations.
  37  *
  38  * These helper types facilitate iterating over class enums, and
  39  * maintaining a type-safe and value-safe matching list of names. The
  40  * code is closely based on the public-domain code by Guilherme
  41  * R. Lampert, found in commit c94c18a of
  42  * https://github.com/glampert/enum_helpers/blob/master/enum_helpers.hpp
  43  * Thanks Guilherme!
  44  *
  45  * NOTE This functionality only works for enumerations of monotonically
  46  * increasing values, starting with the value zero.
  47  *
  48  * Usage examples:
  49  *
  50  *  enum class Foo : int
  51  *  {
  52  *      Bar,
  53  *      Baz,
  54  *      Fooz,
  55  *      Count
  56  *  };
  57  *
  58  *  for (Foo c : EnumerationWrapper<Foo>{})
  59  *  {
  60  *      // 'c' is a constant from Foo
  61  *  }
  62  *
  63  *
  64  *  const EnumerationArray<Foo, std::string> fooStrings = { { "Bar", "Baz", "Fooz" } };
  65  *  std::cout << fooStrings[Foo::Baz];
  66  *  std::cout << fooStrings[Foo::Count]; // Triggers an assertion
  67  *
  68  *  for (Foo c : keysOf(fooStrings))
  69  *  {
  70  *      print(fooStrings[c]);
  71  *  }
  72  *
  73  *  ArrayRef<const std::string> namesRef(fooStrings);
  74  *
  75  * \author Mark Abraham <mark.j.abraham@gmail.com>
  76  * \inlibraryapi
  77  * \ingroup module_utility
  78  */
  79 #ifndef GMX_UTILITY_ENUMHELPERS_H
  80 #define GMX_UTILITY_ENUMHELPERS_H
  81
  82 #include <cstddef>
  83
  84 #include <iterator>
  85 #include <type_traits>
  86
  87 #if __has_include(<boost/stl_interfaces/iterator_interface.hpp>)
  88 #    include <boost/stl_interfaces/iterator_interface.hpp>
  89 #else // fallback for installed headers
  90 #    include <gromacs/external/boost/stl_interfaces/iterator_interface.hpp>
  91 #endif
  92
  93 #include "gromacs/utility/gmxassert.h"
  94
  95 namespace gmx
  96 {
  97
  98 /*! \libinternal
  99  * \brief Allows iterating sequential enumerators.
 100  *
 101  * You can also provide an increment step > 1 if each constant is
 102  * spaced by a larger value.  Terminating constant is assumed to be a
 103  * 'Count' member, which is never iterated. A different name for the
 104  * terminating constant can also be specified on declaration.
 105  *
 106  * NOTE This functionality only works for enumerations of monotonically
 107  * increasing values, starting with the value zero.
 108  *
 109  * See file documentation for usage example.
 110  *
 111  * \tparam  EnumType   The enum (class) type.
 112  * \tparam  Last       Last constant or number thereof (assumes a default 'Count' member).
 113  * \tparam  Step       Step increment.
 114  */
 115 template<typename EnumType, EnumType Last = EnumType::Count, std::ptrdiff_t Step = 1>
 116 class EnumerationIterator final :
 117     public boost::stl_interfaces::iterator_interface<EnumerationIterator<EnumType, Last, Step>, std::random_access_iterator_tag, EnumType>
 118 {
 119 public:
 120     static_assert(std::is_enum_v<EnumType>, "Enumeration iterator must be over an enum type.");
 121     //! Convenience alias
 122     using IntegerType = std::underlying_type_t<EnumType>;
 123
 124     constexpr EnumerationIterator() noexcept : m_current{ 0 } // Assumes 0 is the first constant
 125     {
 126     }
 127     //! Conversion constructor
 128     explicit constexpr EnumerationIterator(const EnumType index) noexcept :
 129         m_current(static_cast<IntegerType>(index))
 130     {
 131     }
 132     //! Addition-assignment operator
 133     constexpr EnumerationIterator& operator+=(std::ptrdiff_t i) noexcept
 134     {
 135         m_current += Step * i;
 136         return *this;
 137     }
 138     //! Dereference operator
 139     constexpr EnumType operator*() const noexcept
 140     {
 141         GMX_ASSERT(m_current < static_cast<IntegerType>(Last), "dereferencing out of range");
 142         return static_cast<EnumType>(m_current);
 143     }
 144     //! Difference operator
 145     constexpr std::ptrdiff_t operator-(const EnumerationIterator other) const noexcept
 146     {
 147         return (static_cast<std::ptrdiff_t>(m_current) - static_cast<std::ptrdiff_t>(other.m_current)) / Step;
 148     }
 149
 150 private:
 151     IntegerType m_current;
 152 };
 153
 154 /*! \libinternal
 155  * \brief Allows constructing iterators for looping over sequential enumerators.
 156  *
 157  * These are particularly useful for range-based for statements.
 158  *
 159  * You can also provide an increment step > 1 if each constant is
 160  * spaced by a larger value.  Terminating constant is assumed to be a
 161  * 'Count' member, which is never iterated. A different name for the
 162  * terminating constant can also be specified on declaration.
 163  *
 164  * See file documentation for usage example.
 165  *
 166  * \tparam  EnumType   The enum (class) type.
 167  * \tparam  Last       Last constant or number thereof (assumes a default 'Count' member).
 168  * \tparam  Step       Step increment.
 169  */
 170 template<typename EnumType, EnumType Last = EnumType::Count, unsigned int Step = 1>
 171 class EnumerationWrapper final
 172 {
 173 public:
 174     //! Convenience alias.
 175     using IteratorType = EnumerationIterator<EnumType, Last, Step>;
 176
 177     //! Functions required for range-based for statements to work.
 178     /*!@{*/
 179     IteratorType begin() const { return IteratorType{}; }
 180     IteratorType end() const { return IteratorType{ Last }; }
 181     /*!@}*/
 182 };
 183
 184 /*! \libinternal
 185  * \brief Wrapper for a C-style array with size and indexing defined
 186  * by an enum. Useful for declaring arrays of enum names for debug
 187  * or other printing. An ArrayRef<DataType> may be constructed from
 188  * an object of this type.
 189  *
 190  * See file documentation for usage example.
 191  *
 192  * \tparam  EnumType   The enum (class) type.
 193  * \tparam  DataType   Type of the data stored in the array.
 194  * \tparam  ArraySize  Size in entries of the array.
 195  */
 196 template<typename EnumType,                   // The enum (class) type.
 197          typename DataType,                   // Type of the data stored in the array.
 198          EnumType ArraySize = EnumType::Count // Size in entries of the array.
 199          >
 200 struct EnumerationArray final
 201 {
 202     //! Convenience alias
 203     using EnumerationWrapperType = EnumerationWrapper<EnumType, ArraySize>;
 204
 205     /*! \brief Data for names.
 206      *
 207      * Data is kept public so we can use direct aggregate
 208      * initialization just like in a plain C-style array. */
 209     DataType m_elements[std::size_t(ArraySize)];
 210
 211     //! Returns an object that provides iterators over the keys.
 212     static constexpr EnumerationWrapperType keys() { return EnumerationWrapperType{}; }
 213     //! Returns the size of the enumeration.
 214     static constexpr std::size_t size() { return std::size_t(ArraySize); }
 215
 216     /*!@{*/
 217     //! Array access with asserts:
 218     DataType& operator[](const std::size_t index)
 219     {
 220         GMX_ASSERT(index < size(), "index out of range");
 221         return m_elements[index];
 222     }
 223     const DataType& operator[](const std::size_t index) const
 224     {
 225         GMX_ASSERT(index < size(), "index out of range");
 226         return m_elements[index];
 227     }
 228
 229     DataType& operator[](const EnumType index)
 230     {
 231         GMX_ASSERT(std::size_t(index) < size(), "index out of range");
 232         return m_elements[std::size_t(index)];
 233     }
 234     const DataType& operator[](const EnumType index) const
 235     {
 236         GMX_ASSERT(std::size_t(index) < size(), "index out of range");
 237         return m_elements[std::size_t(index)];
 238     }
 239     /*!@}*/
 240
 241     /*!@{*/
 242     //! Range iterators (unchecked)
 243     using iterator               = DataType*;
 244     using const_iterator         = const DataType*;
 245     using reverse_iterator       = std::reverse_iterator<iterator>;
 246     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 247     /*!@}*/
 248
 249     /*!@{*/
 250     //! Getters for forward iterators for ranges
 251     iterator       begin() { return &m_elements[0]; }
 252     iterator       end() { return &m_elements[size()]; }
 253     const_iterator begin() const { return &m_elements[0]; }
 254     const_iterator end() const { return &m_elements[size()]; }
 255     /*!@}*/
 256
 257     /*!@{*/
 258     //! Getters for reverse iterators for ranges
 259     reverse_iterator       rbegin() { return reverse_iterator{ end() }; }
 260     reverse_iterator       rend() { return reverse_iterator{ begin() }; }
 261     const_reverse_iterator rbegin() const { return const_reverse_iterator{ end() }; }
 262     const_reverse_iterator rend() const { return const_reverse_iterator{ begin() }; }
 263     /*!@}*/
 264
 265     /*!@{*/
 266     //! Pointers (unchecked)
 267     using pointer       = DataType*;
 268     using const_pointer = const DataType*;
 269     /*!@}*/
 270
 271     //! Returns a const raw pointer to the contents of the array.
 272     const_pointer data() const { return &m_elements[0]; }
 273     //! Returns a raw pointer to the contents of the array.
 274     pointer data() { return &m_elements[0]; }
 275 };
 276
 277 /*! \brief Returns an object that provides iterators over the keys
 278  * associated with \c EnumerationArrayType.
 279  *
 280  * This helper function is useful in contexts where there is an object
 281  * of an EnumerationArray, and we want to use a range-based for loop
 282  * over the keys associated with it, and it would be inconvenient to
 283  * use the very word EnumerationArray<...> type, nor introduce a using
 284  * statement for this purpose. It is legal in C++ to call a static
 285  * member function (such as keys()) via an object rather than the
 286  * type, but clang-tidy warns about that. So instead we make available
 287  * a free function that calls that static method. */
 288 template<typename EnumerationArrayType>
 289 typename EnumerationArrayType::EnumerationWrapperType keysOf(const EnumerationArrayType& /* arrayObject */)
 290 {
 291     return EnumerationArrayType::keys();
 292 }
 293
 294 } // namespace gmx
 295
 296 #endif