src/gromacs/utility/classhelpers.h

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