src/gromacs/utility/any.h

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  35 /*! \libinternal \file
  36  * \brief
  37  * Declares gmx::Any.
  38  *
  39  * \author Teemu Murtola <teemu.murtola@gmail.com>
  40  * \inlibraryapi
  41  * \ingroup module_utility
  42  */
  43 #ifndef GMX_UTILITY_ANY_H
  44 #define GMX_UTILITY_ANY_H
  45
  46 #include <memory>
  47 #include <string>
  48 #include <type_traits>
  49 #include <typeindex>
  50 #include <typeinfo>
  51 #include <utility>
  52
  53 #include "gromacs/utility/gmxassert.h"
  54
  55 namespace gmx
  56 {
  57
  58 /*! \libinternal \brief
  59  * Represents a dynamically typed value of an arbitrary type.
  60  *
  61  * To create a any, either initialize it as empty, or with the create()
  62  * method (or the equivalent constructor, if the type parameter can be deduced
  63  * and is clear to the reader from the context).
  64  *
  65  * To query the type of the contents in the any, use isEmpty(), type(), and
  66  * isType().
  67  *
  68  * To access the value, you need to know the type as a compile-time constant
  69  * (e.g., through branching based on isType()), and then use cast() or
  70  * tryCast().
  71  *
  72  * Methods in this class do not throw unless otherwise indicated.
  73  *
  74  * This provides essentially the same functionality as boost::any.
  75  *
  76  * \ingroup module_utility
  77  */
  78 class Any
  79 {
  80 public:
  81     /*! \brief
  82      * Creates a any that holds the given value.
  83      *
  84      * \throws std::bad_alloc if out of memory.
  85      *
  86      * This method allows explicitly specifying the template argument,
  87      * contrary to the templated constructor.
  88      */
  89     template<typename T>
  90     static Any create(const T& value)
  91     {
  92         return Any(value);
  93     }
  94     /*! \brief
  95      * Creates a any that holds the given value.
  96      *
  97      * \throws std::bad_alloc if out of memory.
  98      *
  99      * In addition to allowing specifying the template argument, this
 100      * method avoids copying when move-construction is possible.
 101      */
 102     template<typename T>
 103     static Any create(T&& value)
 104     {
 105         return Any(std::forward<T>(value));
 106     }
 107
 108     //! Creates an empty any value.
 109     Any() {}
 110     /*! \brief
 111      * Creates a any that holds the given value.
 112      *
 113      * \throws std::bad_alloc if out of memory.
 114      */
 115     template<typename T, typename = std::enable_if_t<!std::is_same_v<T, Any>>>
 116     explicit Any(T&& value) : content_(new Content<std::decay_t<T>>(std::forward<T>(value)))
 117     {
 118     }
 119     /*! \brief
 120      * Creates a deep copy of a any.
 121      *
 122      * \throws std::bad_alloc if out of memory.
 123      */
 124     Any(const Any& other) : content_(other.cloneContent()) {}
 125     //! Move-constructs a any.
 126     Any(Any&& other) noexcept : content_(std::move(other.content_)) {}
 127     /*! \brief
 128      * Assigns the any.
 129      *
 130      * \throws std::bad_alloc if out of memory.
 131      */
 132     Any& operator=(const Any& other)
 133     {
 134         content_ = other.cloneContent();
 135         return *this;
 136     }
 137     //! Move-assigns the any.
 138     Any& operator=(Any&& other) noexcept
 139     {
 140         content_ = std::move(other.content_);
 141         return *this;
 142     }
 143
 144     //! Whether any value is stored.
 145     bool isEmpty() const { return content_ == nullptr; }
 146     //! Returns the dynamic type of the value that is currently stored.
 147     std::type_index type() const
 148     {
 149         const std::type_info& info = !isEmpty() ? content_->typeInfo() : typeid(void);
 150         return std::type_index(info);
 151     }
 152     //! Returns whether the type stored matches the template parameter.
 153     template<typename T>
 154     bool isType() const
 155     {
 156         return !isEmpty() && content_->typeInfo() == typeid(T);
 157     }
 158
 159     /*! \brief
 160      * Tries to get the value as the given type.
 161      *
 162      * \tparam T  Type to get.
 163      * \returns Pointer to the value, or nullptr if the type does not match
 164      *     the stored value.
 165      */
 166     template<typename T>
 167     const T* tryCast() const
 168     {
 169         return isType<T>() ? &static_cast<Content<T>*>(content_.get())->value_ : nullptr;
 170     }
 171     /*! \brief
 172      * Gets the value when the type is known.
 173      *
 174      * \tparam T  Type to get (which must match what the any stores).
 175      *
 176      * Asserts if the any is empty or does not contain the requested type.
 177      */
 178     template<typename T>
 179     const T& cast() const
 180     {
 181         const T* value = tryCast<T>();
 182         GMX_RELEASE_ASSERT(value != nullptr, "Cast to incorrect type");
 183         return *value;
 184     }
 185     /*! \brief
 186      * Tries to get the value as the given type as a non-const pointer.
 187      *
 188      * \tparam T  Type to get.
 189      * \returns Pointer to the value, or nullptr if the type does not match
 190      *     the stored value.
 191      *
 192      * This method allows modifying the value in-place, which is useful
 193      * with more complicated data structures.
 194      */
 195     template<typename T>
 196     T* tryCastRef()
 197     {
 198         return isType<T>() ? &static_cast<Content<T>*>(content_.get())->value_ : nullptr;
 199     }
 200     /*! \brief
 201      * Gets the value when the type is known as a modifiable reference.
 202      *
 203      * \tparam T  Type to get (which must match what the any stores).
 204      *
 205      * Asserts if the any is empty or does not contain the requested type.
 206      */
 207     template<typename T>
 208     T& castRef()
 209     {
 210         T* value = tryCastRef<T>();
 211         GMX_RELEASE_ASSERT(value != nullptr, "Cast to incorrect type");
 212         return *value;
 213     }
 214
 215 private:
 216     class IContent
 217     {
 218     public:
 219         virtual ~IContent() {}
 220         virtual const std::type_info&     typeInfo() const = 0;
 221         virtual std::unique_ptr<IContent> clone() const    = 0;
 222     };
 223
 224     template<typename T>
 225     class Content : public IContent
 226     {
 227     public:
 228         explicit Content(const T& value) : value_(value) {}
 229         explicit Content(T&& value) : value_(std::move(value)) {}
 230
 231         const std::type_info&     typeInfo() const override { return typeid(T); }
 232         std::unique_ptr<IContent> clone() const override
 233         {
 234             return std::make_unique<Content>(value_);
 235         }
 236
 237         T value_;
 238     };
 239
 240     //! Creates a deep copy of the content.
 241     std::unique_ptr<IContent> cloneContent() const
 242     {
 243         return content_ != nullptr ? content_->clone() : nullptr;
 244     }
 245
 246     std::unique_ptr<IContent> content_;
 247 };
 248
 249 //! \cond libapi
 250 /*! \brief
 251  * Converts a Any value to a string.
 252  *
 253  * As the name suggests, only some types of "simple" values (such as int) are
 254  * supported.  Asserts for unsupported types.
 255  *
 256  * \ingroup module_utility
 257  */
 258 std::string simpleValueToString(const Any& value);
 259 //! \endcond
 260
 261 } // namespace gmx
 262
 263 #endif