src/gromacs/compat/pointers.h

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  35
  36 /*! \libinternal \file
  37  * \brief Provides ported functions/classes from gsl/pointers
  38  *
  39  * Adapted from the Guidelines Support Library v2.0.0. at
  40  * https://github.com/Microsoft/GSL
  41  *
  42  * \author Mark Abraham <mark.j.abraham@gmail.com>
  43  * \ingroup module_compat
  44  * \inlibraryapi
  45  */
  46  #ifndef GMX_COMPAT_POINTERS_H
  47  #define GMX_COMPAT_POINTERS_H
  48
  49 #include <type_traits>
  50 #include <utility>
  51
  52 #include "gromacs/utility/gmxassert.h"
  53
  54 namespace gmx
  55 {
  56 namespace compat
  57 {
  58
  59 //! Contract-assurance macros that work like a simple version of the GSL ones
  60 //! \{
  61 #if !defined(__INTEL_COMPILER) || !(__INTEL_COMPILER == 1800 && __INTEL_COMPILER_UPDATE == 0)
  62 #define Expects(cond) GMX_ASSERT((cond), "Precondition violation")
  63 #define Ensures(cond) GMX_ASSERT((cond), "Postcondition violation")
  64 #else
  65 // icc 18.0.0 in a RelWithAssert build has an ICE, even if we directly
  66 // embed the contents of GMX_ASSERT, so it seems the lambda in
  67 // GMX_ASSERT is too complex for it in this use case.
  68 #define Expects(cond)
  69 #define Ensures(cond)
  70 #endif
  71 //! \}
  72
  73 /*! \libinternal
  74  * \brief Restricts a pointer or smart pointer to only hold non-null values.
  75  *
  76  * Has zero size overhead over T.
  77  *
  78  * If T is a pointer (i.e. T == U*) then
  79  * - allow construction from U*
  80  * - disallow construction from nullptr_t
  81  * - disallow default construction
  82  * - ensure construction from null U* fails (only in debug builds)
  83  * - allow implicit conversion to U*
  84  *
  85  * \todo Eliminate this when we require a version of C++ that supports
  86  * std::not_null.
  87  */
  88 template <class T>
  89 class not_null
  90 {
  91     public:
  92         static_assert(std::is_assignable<T &, std::nullptr_t>::value, "T cannot be assigned nullptr.");
  93
  94         //! Move constructor. Asserts in debug mode if \c is nullptr.
  95         template <typename U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type >
  96         constexpr explicit not_null(U &&u) : ptr_(std::forward<U>(u))
  97         {
  98             Expects(ptr_ != nullptr);
  99         }
 100
 101         //! Simple constructor. Asserts in debug mode if \c u is nullptr.
 102         template <typename = typename std::enable_if<!std::is_same<std::nullptr_t, T>::value>::type >
 103         constexpr explicit not_null(T u) : ptr_(u)
 104         {
 105             Expects(ptr_ != nullptr);
 106         }
 107
 108         //! Copy constructor.
 109         template <typename U, typename = typename std::enable_if<std::is_convertible<U, T>::value>::type >
 110         constexpr not_null(const not_null<U> &other) : not_null(other.get())
 111         {
 112         }
 113
 114         //! Default constructors and assignment.
 115         //! \{
 116         not_null(not_null &&other) noexcept        = default;
 117         not_null(const not_null &other)            = default;
 118         not_null &operator=(const not_null &other) = default;
 119         //! \}
 120
 121         //! Getters
 122         //! \{
 123         constexpr T get() const
 124         {
 125             Ensures(ptr_ != nullptr);
 126             return ptr_;
 127         }
 128
 129         constexpr operator T() const { return get(); }
 130         constexpr T operator->() const { return get(); }
 131         //! \}
 132
 133         //! Deleted to prevent compilation when someone attempts to assign a null pointer constant.
 134         //! \{
 135         not_null(std::nullptr_t)            = delete;
 136         not_null &operator=(std::nullptr_t) = delete;
 137         //! \}
 138
 139         //! Deleted unwanted operators because pointers only point to single objects.
 140         //! \{
 141         not_null &operator++()                = delete;
 142         not_null &operator--()                = delete;
 143         not_null operator++(int)              = delete;
 144         not_null operator--(int)              = delete;
 145         not_null &operator+=(std::ptrdiff_t)  = delete;
 146         not_null &operator-=(std::ptrdiff_t)  = delete;
 147         void operator[](std::ptrdiff_t) const = delete;
 148         //! \}
 149
 150     private:
 151         T ptr_;
 152 };
 153
 154 //! Convenience function for making not_null pointers from plain pointers.
 155 template <class T>
 156 not_null<T>
 157 make_not_null(T &&t)
 158 {
 159     return not_null < typename std::remove_cv < typename std::remove_reference<T>::type>::type >{
 160                std::forward<T>(t)
 161     };
 162 }
 163
 164 //! Convenience function for making not_null pointers from smart pointers.
 165 template <class T>
 166 not_null<typename T::pointer>
 167 make_not_null(T &t)
 168 {
 169     return not_null < typename std::remove_reference<T>::type::pointer >{
 170                t.get()
 171     };
 172 }
 173
 174 //! Operators to compare not_null pointers.
 175 //! \{
 176 template <class T, class U>
 177 auto operator==(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() == rhs.get())
 178 {
 179     return lhs.get() == rhs.get();
 180 }
 181
 182 template <class T, class U>
 183 auto operator!=(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() != rhs.get())
 184 {
 185     return lhs.get() != rhs.get();
 186 }
 187
 188 template <class T, class U>
 189 auto operator<(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() < rhs.get())
 190 {
 191     return lhs.get() < rhs.get();
 192 }
 193
 194 template <class T, class U>
 195 auto operator<=(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() <= rhs.get())
 196 {
 197     return lhs.get() <= rhs.get();
 198 }
 199
 200 template <class T, class U>
 201 auto operator>(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() > rhs.get())
 202 {
 203     return lhs.get() > rhs.get();
 204 }
 205
 206 template <class T, class U>
 207 auto operator>=(const not_null<T> &lhs, const not_null<U> &rhs)->decltype(lhs.get() >= rhs.get())
 208 {
 209     return lhs.get() >= rhs.get();
 210 }
 211 //! \}
 212
 213 //! Deleted unwanted arithmetic operators.
 214 //! \{
 215 template <class T, class U>
 216 std::ptrdiff_t operator-(const not_null<T> &, const not_null<U> &) = delete;
 217 template <class T>
 218 not_null<T> operator-(const not_null<T> &, std::ptrdiff_t) = delete;
 219 template <class T>
 220 not_null<T> operator+(const not_null<T> &, std::ptrdiff_t) = delete;
 221 template <class T>
 222 not_null<T> operator+(std::ptrdiff_t, const not_null<T> &) = delete;
 223 //! \}
 224
 225 } // namespace compat
 226 } // namespace gmx
 227
 228 #endif