20 General utilities library [utilities]

20.8 Storage for any type [any]

20.8.5 Non-member functions [any.nonmembers]

void swap(any& x, any& y) noexcept;
Effects: Equivalent to x.swap(y).
template<class T, class... Args> any make_any(Args&&... args);
Effects: Equivalent to: return any(in_­place_­type<T>, std​::​forward<Args>(args)...);
template<class T, class U, class... Args> any make_any(initializer_list<U> il, Args&&... args);
Effects: Equivalent to: return any(in_­place_­type<T>, il, std​::​forward<Args>(args)...);
template<class T> T any_cast(const any& operand); template<class T> T any_cast(any& operand); template<class T> T any_cast(any&& operand);
Let U be the type remove_­cvref_­t<T>.
Mandates: For the first overload, is_­constructible_­v<T, const U&> is true.
For the second overload, is_­constructible_­v<T, U&> is true.
For the third overload, is_­constructible_­v<T, U> is true.
Returns: For the first and second overload, static_­cast<T>(*any_­cast<U>(&operand)).
For the third overload, static_­cast<T>(std​::​move(*any_­cast<U>(&operand))).
Throws: bad_­any_­cast if operand.type() != typeid(remove_­reference_­t<T>).
[Example 1: any x(5); // x holds int assert(any_cast<int>(x) == 5); // cast to value any_cast<int&>(x) = 10; // cast to reference assert(any_cast<int>(x) == 10); x = "Meow"; // x holds const char* assert(strcmp(any_cast<const char*>(x), "Meow") == 0); any_cast<const char*&>(x) = "Harry"; assert(strcmp(any_cast<const char*>(x), "Harry") == 0); x = string("Meow"); // x holds string string s, s2("Jane"); s = move(any_cast<string&>(x)); // move from any assert(s == "Meow"); any_cast<string&>(x) = move(s2); // move to any assert(any_cast<const string&>(x) == "Jane"); string cat("Meow"); const any y(cat); // const y holds string assert(any_cast<const string&>(y) == cat); any_cast<string&>(y); // error: cannot any_­cast away const — end example]
template<class T> const T* any_cast(const any* operand) noexcept; template<class T> T* any_cast(any* operand) noexcept;
Returns: If operand != nullptr && operand->type() == typeid(T), a pointer to the object contained by operand; otherwise, nullptr.
[Example 2: bool is_string(const any& operand) { return any_cast<string>(&operand) != nullptr; } — end example]