src/gromacs/utility/enumerationhelpers.h

   1 /*
   2  * This file is part of the GROMACS molecular simulation package.
   3  *
   4  * Copyright (c) 2019, by the GROMACS development team, led by
   5  * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
   6  * and including many others, as listed in the AUTHORS file in the
   7  * top-level source directory and at http://www.gromacs.org.
   8  *
   9  * GROMACS is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public License
  11  * as published by the Free Software Foundation; either version 2.1
  12  * of the License, or (at your option) any later version.
  13  *
  14  * GROMACS is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with GROMACS; if not, see
  21  * http://www.gnu.org/licenses, or write to the Free Software Foundation,
  22  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA.
  23  *
  24  * If you want to redistribute modifications to GROMACS, please
  25  * consider that scientific software is very special. Version
  26  * control is crucial - bugs must be traceable. We will be happy to
  27  * consider code for inclusion in the official distribution, but
  28  * derived work must not be called official GROMACS. Details are found
  29  * in the README & COPYING files - if they are missing, get the
  30  * official version at http://www.gromacs.org.
  31  *
  32  * To help us fund GROMACS development, we humbly ask that you cite
  33  * the research papers on the package. Check out http://www.gromacs.org.
  34  */
  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
  51  *  {
  52  *      Bar, Baz, Fooz,
  53  *      Count
  54  *  };
  55  *
  56  *  EnumerationWrapper<Foo> iter;
  57  *
  58  *  for (Foo c : iter)
  59  *  {
  60  *      // 'c' is a constant from Foo
  61  *  }
  62  *
  63  *  const EnumerationArray<Foo, std::string> fooStrings = { { "Bar", "Baz", "Fooz" } };
  64  *
  65  *  for (Foo c : keysOf(fooStrings))
  66  *  {
  67  *      print(fooStrings[c]);
  68  *  }
  69  *
  70  *  ArrayRef<const std::string> namesRef(fooStrings);
  71  *
  72  * \author Mark Abraham <mark.j.abraham@gmail.com>
  73  * \inlibraryapi
  74  * \ingroup module_utility
  75  */
  76 #ifndef GMX_UTILITY_ENUMHELPERS_H
  77 #define GMX_UTILITY_ENUMHELPERS_H
  78
  79 #include <cstddef>
  80
  81 #include <iterator>
  82 #include <type_traits>
  83
  84 #include "gromacs/utility/gmxassert.h"
  85
  86 namespace gmx
  87 {
  88
  89 /*! \libinternal
  90  * \brief Allows iterating sequential enumerators.
  91  *
  92  * You can also provide an increment step > 1 if each constant is
  93  * spaced by a larger value.  Terminating constant is assumed to be a
  94  * 'Count' member, which is never iterated. A different name for the
  95  * terminating constant can also be specified on declaration.
  96  *
  97  * NOTE This functionality only works for enumerations of monotonically
  98  * increasing values, starting with the value zero.
  99  *
 100  * See file documentation for usage example.
 101  *
 102  * \tparam  EnumType   The enum (class) type.
 103  * \tparam  Last       Last constant or number thereof (assumes a default 'Count' member).
 104  * \tparam  Step       Step increment.
 105  */
 106 template
 107 <
 108     typename EnumType,
 109     EnumType Last     = EnumType::Count,
 110     unsigned int Step = 1
 111 >
 112 class EnumerationIterator final
 113 {
 114     public:
 115         //! Convenience alias
 116         using IntegerType = std::underlying_type_t<EnumType>;
 117
 118         /*! \name Iterator type traits
 119          * Satisfies the requirements for STL forward iterator.
 120          * \{
 121          */
 122         using iterator_category = std::forward_iterator_tag;
 123         using value_type        = EnumType;
 124         using difference_type   = std::ptrdiff_t;
 125         using pointer           = EnumType*;
 126         using reference         = EnumType&;
 127         //! \}
 128
 129         constexpr EnumerationIterator() noexcept :
 130         m_current { 0 } // Assumes 0 is the first constant
 131         { }
 132         //! Copy constructor
 133         constexpr EnumerationIterator(const EnumType index) noexcept
 134         : m_current(static_cast<IntegerType>(index))
 135         { }
 136         //! Pre-increment operator
 137         EnumerationIterator operator++()
 138         {
 139             m_current += Step;
 140             return *this;
 141         }
 142         //! Post-increment operator
 143         EnumerationIterator operator++(int)
 144         {
 145             EnumerationIterator old_val { *this };
 146             m_current += Step;
 147             return old_val;
 148         }
 149         //! Dereference operator
 150         EnumType operator*() const
 151         {
 152             GMX_ASSERT(m_current < static_cast<IntegerType>(Last), "dereferencing out of range");
 153             return static_cast<EnumType>(m_current);
 154         }
 155
 156         /*!@{*/
 157         //! Comparision operators
 158         bool operator== (const EnumerationIterator other) const noexcept { return m_current == other.m_current; }
 159         bool operator!= (const EnumerationIterator other) const noexcept { return m_current != other.m_current; }
 160         bool operator<  (const EnumerationIterator other) const noexcept { return m_current <  other.m_current; }
 161         bool operator>  (const EnumerationIterator other) const noexcept { return m_current >  other.m_current; }
 162         bool operator<= (const EnumerationIterator other) const noexcept { return m_current <= other.m_current; }
 163         bool operator>= (const EnumerationIterator other) const noexcept { return m_current >= other.m_current; }
 164         /*!@}*/
 165
 166     private:
 167         IntegerType m_current;
 168 };
 169
 170 /*! \libinternal
 171  * \brief Allows constructing iterators for looping over sequential enumerators.
 172  *
 173  * These are particularly useful for range-based for statements.
 174  *
 175  * You can also provide an increment step > 1 if each constant is
 176  * spaced by a larger value.  Terminating constant is assumed to be a
 177  * 'Count' member, which is never iterated. A different name for the
 178  * terminating constant can also be specified on declaration.
 179  *
 180  * See file documentation for usage example.
 181  *
 182  * \tparam  EnumType   The enum (class) type.
 183  * \tparam  Last       Last constant or number thereof (assumes a default 'Count' member).
 184  * \tparam  Step       Step increment.
 185  */
 186 template
 187 <
 188     typename EnumType,
 189     EnumType Last     = EnumType::Count,
 190     unsigned int Step = 1
 191 >
 192 class EnumerationWrapper final
 193 {
 194     public:
 195         //! Convenience alias.
 196         using IteratorType = EnumerationIterator<EnumType, Last, Step>;
 197
 198         //! Functions required for range-based for statements to work.
 199         /*!@{*/
 200         IteratorType begin() const { return IteratorType {}; }
 201         IteratorType end()   const { return IteratorType { Last }; }
 202         /*!@}*/
 203 };
 204
 205 /*! \libinternal
 206  * \brief Wrapper for a C-style array with size and indexing defined
 207  * by an enum. Useful for declaring arrays of enum names for debug
 208  * or other printing. An ArrayRef<DataType> may be constructed from
 209  * an object of this type.
 210  *
 211  * See file documentation for usage example.
 212  *
 213  * \tparam  EnumType   The enum (class) type.
 214  * \tparam  DataType   Type of the data stored in the array.
 215  * \tparam  ArraySize  Size in entries of the array.
 216  */
 217 template
 218 <
 219     typename EnumType,                   // The enum (class) type.
 220     typename DataType,                   // Type of the data stored in the array.
 221     EnumType ArraySize = EnumType::Count // Size in entries of the array.
 222 >
 223 struct EnumerationArray final
 224 {
 225     //! Convenience alias
 226     using EnumerationWrapperType = EnumerationWrapper<EnumType, ArraySize>;
 227
 228     /*! \brief Data for names.
 229      *
 230      * Data is kept public so we can use direct aggregate
 231      * initialization just like in a plain C-style array. */
 232     DataType m_elements[std::size_t(ArraySize)];
 233
 234     //! Returns an object that provides iterators over the keys.
 235     static constexpr EnumerationWrapperType keys() { return EnumerationWrapperType {}; }
 236     //! Returns the size of the enumeration.
 237     static constexpr std::size_t size() { return std::size_t(ArraySize); }
 238
 239     /*!@{*/
 240     //! Array access with asserts:
 241     DataType &operator[](const std::size_t index)
 242     {
 243         GMX_ASSERT(index < size(), "index out of range");
 244         return m_elements[index];
 245     }
 246     const DataType &operator[](const std::size_t index) const
 247     {
 248         GMX_ASSERT(index < size(), "index out of range");
 249         return m_elements[index];
 250     }
 251
 252     DataType &operator[](const EnumType index)
 253     {
 254         GMX_ASSERT(std::size_t(index) < size(), "index out of range");
 255         return m_elements[std::size_t(index)];
 256     }
 257     const DataType &operator[](const EnumType index) const
 258     {
 259         GMX_ASSERT(std::size_t(index) < size(), "index out of range");
 260         return m_elements[std::size_t(index)];
 261     }
 262     /*!@}*/
 263
 264     /*!@{*/
 265     //! Range iterators (unchecked)
 266     using iterator               = DataType *;
 267     using const_iterator         = const DataType *;
 268     using reverse_iterator       = std::reverse_iterator<iterator>;
 269     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 270     /*!@}*/
 271
 272     /*!@{*/
 273     //! Getters for forward iterators for ranges
 274     iterator               begin()        { return &m_elements[0];      }
 275     iterator               end()          { return &m_elements[size()]; }
 276     const_iterator         begin()  const { return &m_elements[0];      }
 277     const_iterator         end()    const { return &m_elements[size()]; }
 278     /*!@}*/
 279
 280     /*!@{*/
 281     //! Getters for reverse iterators for ranges
 282     reverse_iterator       rbegin()       { return reverse_iterator { end() }; }
 283     reverse_iterator       rend()         { return reverse_iterator { begin() }; }
 284     const_reverse_iterator rbegin() const { return const_reverse_iterator { end() }; }
 285     const_reverse_iterator rend()   const { return const_reverse_iterator { begin() }; }
 286     /*!@}*/
 287
 288     /*!@{*/
 289     //! Pointers (unchecked)
 290     using pointer       = DataType *;
 291     using const_pointer = const DataType *;
 292     /*!@}*/
 293
 294     //! Returns a const raw pointer to the contents of the array.
 295     const_pointer data() const { return &m_elements[0]; }
 296     //! Returns a raw pointer to the contents of the array.
 297     pointer data() { return &m_elements[0]; }
 298 };
 299
 300 /*! \brief Returns an object that provides iterators over the keys
 301  * associated with \c EnumerationArrayType.
 302  *
 303  * This helper function is useful in contexts where there is an object
 304  * of an EnumerationArray, and we want to use a range-based for loop
 305  * over the keys associated with it, and it would be inconvenient to
 306  * use the very word EnumerationArray<...> type, nor introduce a using
 307  * statement for this purpose. It is legal in C++ to call a static
 308  * member function (such as keys()) via an object rather than the
 309  * type, but clang-tidy warns about that. So instead we make available
 310  * a free function that calls that static method. */
 311 template <typename EnumerationArrayType>
 312 typename EnumerationArrayType::EnumerationWrapperType keysOf(const EnumerationArrayType & /* arrayObject */)
 313 {
 314     return EnumerationArrayType::keys();
 315 }
 316
 317 } // namespace gmx
 318
 319 #endif