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35 /*! \libinternal \file
37 * Declares gmx::Variant.
39 * \author Teemu Murtola <teemu.murtola@gmail.com>
41 * \ingroup module_utility
43 #ifndef GMX_UTILITY_VARIANT_H
44 #define GMX_UTILITY_VARIANT_H
48 #include <type_traits>
53 #include "gromacs/utility/gmxassert.h"
58 /*! \libinternal \brief
59 * Represents a dynamically typed value of an arbitrary type.
61 * To create a variant, 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).
65 * To query the type of the contents in the variant, use isEmpty(), type(), and
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
72 * Methods in this class do not throw unless otherwise indicated.
74 * This provides essentially the same functionality as boost::any.
76 * \ingroup module_utility
82 * Creates a variant that holds the given value.
84 * \throws std::bad_alloc if out of memory.
86 * This method allows explicitly specifying the template argument,
87 * contrary to the templated constructor.
90 static Variant create(const T &value) { return Variant(value); }
92 * Creates a variant that holds the given value.
94 * \throws std::bad_alloc if out of memory.
96 * In addition to allowing specifying the template argument, this
97 * method avoids copying when move-construction is possible.
100 static Variant create(T &&value) { return Variant(std::move(value)); }
102 //! Creates an empty variant value.
105 * Creates a variant that holds the given value.
107 * \throws std::bad_alloc if out of memory.
109 template <typename T>
110 explicit Variant(const T &value)
111 : content_(new Content<typename std::decay<T>::type>(value))
115 * Creates a variant that holds the given value.
117 * \throws std::bad_alloc if out of memory.
119 template <typename T>
120 explicit Variant(T &&value)
121 : content_(new Content<typename std::decay<T>::type>(std::move(value)))
125 * Creates a deep copy of a variant.
127 * \throws std::bad_alloc if out of memory.
129 Variant(const Variant &other) : content_(other.cloneContent()) {}
130 //! Move-constructs a variant.
131 Variant(Variant &&other) noexcept : content_(std::move(other.content_)) {}
133 * Assigns the variant.
135 * \throws std::bad_alloc if out of memory.
137 Variant &operator=(const Variant &other)
139 content_.reset(other.cloneContent());
142 //! Move-assigns the variant.
143 Variant &operator=(Variant &&other) noexcept
145 content_ = std::move(other.content_);
149 //! Whether any value is stored.
150 bool isEmpty() const { return content_ == nullptr; }
151 //! Returns the dynamic type of the value that is currently stored.
152 std::type_index type() const
154 const std::type_info &info
155 = !isEmpty() ? content_->typeInfo() : typeid(void);
156 return std::type_index(info);
158 //! Returns whether the type stored matches the template parameter.
159 template <typename T>
162 return !isEmpty() && content_->typeInfo() == typeid(T);
166 * Tries to get the value as the given type.
168 * \tparam T Type to get.
169 * \returns Pointer to the value, or nullptr if the type does not match
172 template <typename T>
173 const T *tryCast() const
175 return isType<T>() ? &static_cast<Content<T> *>(content_.get())->value_ : nullptr;
178 * Gets the value when the type is known.
180 * \tparam T Type to get (which must match what the variant stores).
182 * Asserts if the variant is empty or does not contain the requested type.
184 template <typename T>
185 const T &cast() const
187 const T *value = tryCast<T>();
188 GMX_RELEASE_ASSERT(value != nullptr, "Cast to incorrect type");
192 * Tries to get the value as the given type as a non-const pointer.
194 * \tparam T Type to get.
195 * \returns Pointer to the value, or nullptr if the type does not match
198 * This method allows modifying the value in-place, which is useful
199 * with more complicated data structures.
201 template <typename T>
204 return isType<T>() ? &static_cast<Content<T> *>(content_.get())->value_ : nullptr;
207 * Gets the value when the type is known as a modifiable reference.
209 * \tparam T Type to get (which must match what the variant stores).
211 * Asserts if the variant is empty or does not contain the requested type.
213 template <typename T>
216 T *value = tryCastRef<T>();
217 GMX_RELEASE_ASSERT(value != nullptr, "Cast to incorrect type");
225 virtual ~IContent() {}
226 virtual const std::type_info &typeInfo() const = 0;
227 virtual IContent *clone() const = 0;
230 template <typename T>
231 class Content : public IContent
234 explicit Content(const T &value) : value_(value) {}
235 explicit Content(T &&value) : value_(std::move(value)) {}
237 virtual const std::type_info &typeInfo() const { return typeid(T); }
238 virtual IContent *clone() const { return new Content(value_); }
243 //! Creates a deep copy of the content.
244 IContent *cloneContent() const
246 return content_ != nullptr ? content_->clone() : nullptr;
249 std::unique_ptr<IContent> content_;
254 * Converts a Variant value to a string.
256 * As the name suggests, only some types of "simple" values (such as int) are
257 * supported. Asserts for unsupported types.
259 * \ingroup module_utility
261 std::string simpleValueToString(const Variant &value);