src/gromacs/utility/classhelpers.h

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  36 /*! \file
  37  * \brief
  38  * Declares common utility classes and macros.
  39  *
  40  * This header contains helpers used to implement classes in the library.
  41  * It is installed, because the helpers are used in installed headers, but
  42  * typically users of the library should not need to be aware of these helpers.
  43  *
  44  * \author Teemu Murtola <teemu.murtola@gmail.com>
  45  * \inlibraryapi
  46  * \ingroup module_utility
  47  */
  48 #ifndef GMX_UTILITY_CLASSHELPERS_H
  49 #define GMX_UTILITY_CLASSHELPERS_H
  50
  51 #include <memory>
  52
  53 namespace gmx
  54 {
  55
  56 #ifdef DOXYGEN
  57 /*! \brief
  58  * Macro to declare a class non-copyable and non-assignable.
  59  *
  60  * For consistency, should appear last in the class declaration.
  61  *
  62  * \ingroup module_utility
  63  */
  64 #    define GMX_DISALLOW_COPY_AND_ASSIGN(ClassName)
  65 #else
  66 #    define GMX_DISALLOW_COPY_AND_ASSIGN(ClassName)      \
  67         ClassName& operator=(const ClassName&) = delete; \
  68         ClassName(const ClassName&)            = delete
  69 #endif
  70 #ifdef DOXYGEN
  71 /*! \brief
  72  * Macro to declare a class non-copyable, non-movable, non-copy-assignable and
  73  * non-move-assignable.
  74  *
  75  * For consistency, should appear last in the class declaration.
  76  *
  77  * \ingroup module_utility
  78  */
  79 #    define GMX_DISALLOW_COPY_MOVE_AND_ASSIGN(ClassName)
  80 #else
  81 #    define GMX_DISALLOW_COPY_MOVE_AND_ASSIGN(ClassName)                                                            \
  82         ClassName& operator=(const ClassName&) = delete;                                                            \
  83         ClassName(const ClassName&)            = delete;                                                            \
  84         ClassName& operator=(ClassName&&) = delete; /* NOLINT(misc-macro-parentheses,bugprone-macro-parentheses) */ \
  85         ClassName(ClassName&&) = delete /* NOLINT(misc-macro-parentheses,bugprone-macro-parentheses) */
  86 #endif
  87 /*! \brief
  88  * Macro to declare a class non-assignable.
  89  *
  90  * For consistency, should appear last in the class declaration.
  91  *
  92  * \ingroup module_utility
  93  */
  94 #define GMX_DISALLOW_ASSIGN(ClassName) ClassName& operator=(const ClassName&) = delete
  95
  96 // clang-format off
  97 #ifdef DOXYGEN
  98 /*! \brief
  99  * Macro to declare default constructors
 100  *
 101  * Intended for copyable interfaces or bases classes which require to create custom
 102  * destructor (e.g. protected or virtual) but need the default constructors.
 103  *
 104  * \ingroup module_utility
 105  */
 106 #    define GMX_DEFAULT_CONSTRUCTORS(ClassName)
 107 #else
 108 #    define GMX_DEFAULT_CONSTRUCTORS(ClassName)                                                                           \
 109         ClassName() = default;                                                                                            \
 110         ClassName& operator=(const ClassName&) = default; /* NOLINT(misc-macro-parentheses,bugprone-macro-parentheses) */ \
 111         ClassName(const ClassName&) = default;                                                                            \
 112         ClassName& operator=(ClassName&&) = default; /* NOLINT(misc-macro-parentheses,bugprone-macro-parentheses) */      \
 113         ClassName(ClassName&&) = default /* NOLINT(misc-macro-parentheses,bugprone-macro-parentheses) */
 114 #endif
 115 //clang-format on
 116
 117 /*! \brief
 118  * Helper class to manage a pointer to a private implementation class.
 119  *
 120  * This helper provides the following benefits (all but the last could also be
 121  * achieved with std::unique_ptr):
 122  *  - Automatic memory management: the implementation pointer is freed in
 123  *    the destructor automatically.  If the destructor is not declared or is
 124  *    defined inline in the header file, a compilation error occurs instead
 125  *    of a memory leak or undefined behavior.
 126  *  - Exception safety in constructors: the implementation pointer is freed
 127  *    correctly even if the constructor of the containing class throws after
 128  *    the implementation class is constructed.
 129  *  - Copy and/or assignment is automatically disallowed if explicit copy
 130  *    constructor and/or assignment operator is not provided.
 131  *  - Compiler helps to manage const-correctness: in const methods, it is not
 132  *    possible to change the implementation class.
 133  *
 134  * Move construction and assignment are also disallowed, but can be enabled by
 135  * providing explicit move constructor and/or assignment.
 136  *
 137  * Intended use:
 138  * \code
 139    // In exampleclass.h
 140    class ExampleClass
 141    {
 142        public:
 143            ExampleClass();
 144            ~ExampleClass(); // Must be defined, must not be defined inline
 145
 146            // <...>
 147
 148        private:
 149            class Impl;
 150
 151            PrivateImplPointer<Impl> impl_;
 152    };
 153
 154    // In exampleclass.cpp
 155
 156    // <definition of ExampleClass::Impl>
 157
 158    ExampleClass::ExampleClass()
 159        : impl_(new Impl)
 160    {
 161    }
 162
 163    ExampleClass::~ExampleClass()
 164    {
 165    }
 166    \endcode
 167  *
 168  * Note that ExampleClass::~ExampleClass cannot be declared inline (or
 169  * generated by the compiler) because the implementation of impl_
 170  * requires that ExampleClass::Impl be known in size, whereas it has
 171  * only been forward declared. Only the translation unit where
 172  * ExampleClass::Impl is declared can define the destructor for
 173  * ExampleClass (which may be defaulted).
 174  *
 175  * \inlibraryapi
 176  * \ingroup module_utility
 177  */
 178 template<class Impl>
 179 class PrivateImplPointer
 180 {
 181 public:
 182     //! Allow implicit initialization from nullptr to support comparison.
 183     PrivateImplPointer(std::nullptr_t) : ptr_(nullptr) {}
 184     //! Initialize with the given implementation class.
 185     explicit PrivateImplPointer(Impl* ptr) : ptr_(ptr) {}
 186     //! \cond
 187     // Explicitly declared to work around MSVC problems.
 188     PrivateImplPointer(PrivateImplPointer&& other) noexcept : ptr_(std::move(other.ptr_)) {}
 189     PrivateImplPointer& operator=(PrivateImplPointer&& other) noexcept
 190     {
 191         ptr_ = std::move(other.ptr_);
 192         return *this;
 193     }
 194     //! \endcond
 195
 196     /*! \brief
 197      * Sets a new implementation class and destructs the previous one.
 198      *
 199      * Needed, e.g., to implement lazily initializable or copy-assignable
 200      * classes.
 201      */
 202     void reset(Impl* ptr) { ptr_.reset(ptr); }
 203     //! Access the raw pointer.
 204     Impl* get() { return ptr_.get(); }
 205     //! Access the implementation class as with a raw pointer.
 206     Impl* operator->() { return ptr_.get(); }
 207     //! Access the implementation class as with a raw pointer.
 208     Impl& operator*() { return *ptr_; }
 209     //! Access the implementation class as with a raw pointer.
 210     const Impl* operator->() const { return ptr_.get(); }
 211     //! Access the implementation class as with a raw pointer.
 212     const Impl& operator*() const { return *ptr_; }
 213
 214     //! Allows testing whether the implementation is initialized.
 215     explicit operator bool() const { return ptr_ != nullptr; }
 216
 217     //! Tests for equality (mainly useful against nullptr).
 218     bool operator==(const PrivateImplPointer& other) const { return ptr_ == other.ptr_; }
 219     //! Tests for inequality (mainly useful against nullptr).
 220     bool operator!=(const PrivateImplPointer& other) const { return ptr_ != other.ptr_; }
 221
 222 private:
 223     std::unique_ptr<Impl> ptr_;
 224
 225     // Copy construction and assignment disabled by the unique_ptr member.
 226 };
 227
 228 } // namespace gmx
 229
 230 #endif