src/gromacs/utility/arrayref.h

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  35 /*! \file
  36  * \brief
  37  * Declares gmx::ArrayRef
  38  *
  39  * \author Teemu Murtola <teemu.murtola@gmail.com>
  40  * \author Mark Abraham <mark.j.abraham@gmail.com>
  41  * \author Roland Schulz <roland.schulz@intel.com>
  42  * \author Berk Hess <hess@kth.se>
  43  * \inpublicapi
  44  * \ingroup module_utility
  45  */
  46 #ifndef GMX_UTILITY_ARRAYREF_H
  47 #define GMX_UTILITY_ARRAYREF_H
  48
  49 #include <cstddef>
  50
  51 #include <array>
  52 #include <iterator>
  53 #include <stdexcept>
  54 #include <utility>
  55 #include <vector>
  56
  57 #include "gromacs/utility/gmxassert.h"
  58
  59 namespace gmx
  60 {
  61
  62 /*! \brief STL-like interface to a C array of T (or part
  63  * of a std container of T).
  64  *
  65  * \tparam T  Value type of elements.
  66  *
  67  * This class provides an interface similar to \c std::vector<T, A>, with the
  68  * following main differences:
  69  *  - This class does not have its own storage.  Instead, it references an
  70  *    existing array of values (either a C-style array or part of an existing
  71  *    std::vector<T, A> or std::array<T>).
  72  *  - It is only possible to modify the values themselves through ArrayRef;
  73  *    it is not possible to add or remove values.
  74  *  - Copying objects of this type is cheap, and the copies behave identically
  75  *    to the original object: the copy references the same set of values.
  76  *
  77  * This class is useful for writing wrappers that expose a view of the
  78  * internal data stored as a single vector/array, which can be a whole
  79  * or part of the underlying storage.
  80  *
  81  * Methods in this class do not throw, except where indicated.
  82  *
  83  * Note that due to a Doxygen limitation, the constructor that takes a C array
  84  * whose size is known at compile time does not appear in the documentation.
  85  *
  86  * To refer to const data of type T, ArrayRef<const T> is used. For both const
  87  * and non-const std::vector and std::array an ArrayRef view can be created.
  88  * Attempting to create a non-const ArrayRef of a const vector/array will result
  89  * in a compiler error in the respective constructor.
  90  *
  91  * For SIMD types there is template specialization available
  92  * (e.g. ArrayRef<SimdReal>) in gromacs/simd/simd_memory.h which should have
  93  * the same functionality as much as possible.
  94  *
  95  * \todo
  96  * This class is not complete. There are likely also methods missing (not
  97  * required for current usage).
  98  *
  99  * \inpublicapi
 100  * \ingroup module_utility
 101  */
 102 template <typename T>
 103 class ArrayRef
 104 {
 105     public:
 106         //! Type of values stored in the reference.
 107         typedef T         value_type;
 108         //! Type for representing size of the reference.
 109         typedef size_t    size_type;
 110         //! Type for representing difference between two indices.
 111         typedef ptrdiff_t difference_type;
 112         //! Const reference to an element.
 113         typedef const T  &const_reference;
 114         //! Const pointer to an element.
 115         typedef const T  *const_pointer;
 116         //! Const iterator type to an element.
 117         typedef const T  *const_iterator;
 118         //! Reference to an element.
 119         typedef T        &reference;
 120         //! Pointer to an element.
 121         typedef T        *pointer;
 122         //! Iterator type to an element.
 123         typedef T        *iterator;
 124         //! Standard reverse iterator.
 125         typedef std::reverse_iterator<iterator>       reverse_iterator;
 126         //! Standard reverse iterator.
 127         typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
 128
 129         /*! \brief
 130          * Constructs an empty reference.
 131          */
 132         ArrayRef() : begin_(nullptr), end_(nullptr) {}
 133         /*! \brief
 134          * Constructs a reference to a container or reference
 135          *
 136          * \param[in] o container to reference.
 137          *
 138          * Can be used to create a reference to a whole vector, std::array or
 139          * an ArrayRef. The destination has to have a convertible pointer type
 140          * (identical besides const or base class).
 141          *
 142          * Passed container must remain valid and not be reallocated for the
 143          * lifetime of this object.
 144          *
 145          * This constructor is not explicit to allow directly passing
 146          * a container to a method that takes ArrayRef.
 147          */
 148         template<typename U,
 149                  typename = std::enable_if_t<
 150                          std::is_convertible<typename std::remove_reference_t<U>::pointer,
 151                                              pointer>::value> >
 152         ArrayRef(U &&o) : begin_(o.data()), end_(o.data()+o.size()) {}
 153         /*! \brief
 154          * Constructs a reference to a particular range.
 155          *
 156          * \param[in] begin  Pointer to the beginning of a range.
 157          * \param[in] end    Pointer to the end of a range.
 158          *
 159          * Passed pointers must remain valid for the lifetime of this object.
 160          */
 161         ArrayRef(pointer begin, pointer end)
 162             : begin_(begin), end_(end)
 163         {
 164             GMX_ASSERT(end >= begin, "Invalid range");
 165         }
 166         //! \cond
 167         // Doxygen 1.8.5 doesn't parse the declaration correctly...
 168         /*! \brief
 169          * Constructs a reference to a C array.
 170          *
 171          * \param[in] array  C array to reference.
 172          * \tparam    count  Deduced number of elements in \p array.
 173          *
 174          * This constructor can only be used with a real array (not with a
 175          * pointer).  It constructs a reference to the whole array, without
 176          * a need to pass the number of elements explicitly.  The compiler
 177          * must be able to deduce the array size.
 178          *
 179          * Passed array must remain valid for the lifetime of this object.
 180          *
 181          * This constructor is not explicit to allow directly passing
 182          * a C array to a function that takes an ArrayRef parameter.
 183          */
 184         template <size_t count>
 185         ArrayRef(value_type (&array)[count])
 186             : begin_(array), end_(array + count)
 187         {
 188         }
 189         //! \endcond
 190
 191         //! Returns a reference to part of the memory.
 192         ArrayRef subArray(size_type start, size_type count) const
 193         {
 194             return {begin_+start, begin_+start+count};
 195         }
 196         //! Returns an iterator to the beginning of the reference.
 197         iterator begin() const { return begin_; }
 198         //! Returns an iterator to the end of the reference.
 199         iterator end() const { return end_; }
 200         //! Returns an iterator to the reverse beginning of the reference.
 201         reverse_iterator rbegin() const { return reverse_iterator(end()); }
 202         //! Returns an iterator to the reverse end of the reference.
 203         reverse_iterator rend() const { return reverse_iterator(begin()); }
 204
 205         /*! \brief Returns the size of the reference.
 206          *
 207          * \note Use ssize for any expression involving arithmetic operations
 208              (including loop indices).
 209          */
 210         size_type size() const { return end_ - begin_; }
 211         //! Returns the signed size of the reference.
 212         index ssize() const { return size(); }
 213         //! Identical to size().
 214         size_type capacity() const { return end_ - begin_; }
 215         //! Whether the reference refers to no memory.
 216         bool empty() const { return begin_ == end_; }
 217
 218         //! Access an element.
 219         reference operator[](size_type n) const { return begin_[n]; }
 220         //! Access an element (throws on out-of-range error).
 221         reference at(size_type n) const
 222         {
 223             if (n >= size())
 224             {
 225                 throw std::out_of_range("Vector index out of range");
 226             }
 227             return begin_[n];
 228         }
 229         //! Returns the first element.
 230         reference front() const { return *begin_; }
 231         //! Returns the first element.
 232         reference back() const { return *(end_ - 1); }
 233
 234         //! Returns a raw pointer to the contents of the array.
 235         pointer data() const { return begin_; }
 236
 237         /*! \brief
 238          * Swaps referenced memory with the other object.
 239          *
 240          * The actual memory areas are not modified, only the references are
 241          * swapped.
 242          */
 243         void swap(ArrayRef<T> &other)
 244         {
 245             std::swap(begin_, other.begin_);
 246             std::swap(end_, other.end_);
 247         }
 248
 249     private:
 250         pointer           begin_;
 251         pointer           end_;
 252 };
 253
 254 //! \copydoc ArrayRef::fromArray()
 255 //! \related ArrayRef
 256 template <typename T>
 257 ArrayRef<T> arrayRefFromArray(T *begin, size_t size)
 258 {
 259     return ArrayRef<T>(begin, begin+size);
 260 }
 261
 262 //! \copydoc ArrayRef::fromArray()
 263 //! \related ArrayRef
 264 template <typename T>
 265 ArrayRef<const T> constArrayRefFromArray(const T *begin, size_t size)
 266 {
 267     return ArrayRef<const T>(begin, begin+size);
 268 }
 269
 270 /*! \brief
 271  * Create ArrayRef from container with type deduction
 272  *
 273  * \see ArrayRef
 274  */
 275 template <typename T>
 276 ArrayRef < std::conditional_t < std::is_const<T>::value,
 277 const typename T::value_type,
 278 typename T::value_type>>
 279 makeArrayRef(T &c)
 280 {
 281     return c;
 282 }
 283
 284 /*! \brief
 285  * Create ArrayRef to const T from container with type deduction
 286  *
 287  * \see ArrayRef
 288  */
 289 template <typename T>
 290 ArrayRef<const typename T::value_type> makeConstArrayRef(const T &c)
 291 {
 292     return c;
 293 }
 294
 295 /*! \brief
 296  * Simple swap method for ArrayRef objects.
 297  *
 298  * \see ArrayRef::swap()
 299  *
 300  * \ingroup module_utility
 301  */
 302 template <typename T>
 303 void swap(ArrayRef<T> &a, ArrayRef<T> &b)
 304 {
 305     a.swap(b);
 306 }
 307
 308 /*! \brief Return a vector that is a copy of an ArrayRef.
 309  *
 310  * This makes it convenient, clear, and performant (the compiler will
 311  * either do RVO to elide the temporary, or invoke the move constructor
 312  * taking the unnamed temporary) to write a declaration like
 313  *
 314  *   auto v = copyOf(arrayRef);
 315  *
 316  * \ingroup module_utility
 317  */
 318 template <typename T>
 319 std::vector<T> copyOf(const ArrayRef<const T> &arrayRef)
 320 {
 321     return std::vector<T>(arrayRef.begin(), arrayRef.end());
 322 }
 323
 324 } // namespace gmx
 325
 326 #endif