22 General utilities library [utilities]

22.7 Storage for any type [any]

22.7.5 Non-member functions [any.nonmembers]

void swap(any& x, any& y) noexcept;

Effects: Equivalent to x.swap(y).

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template<class T, class... Args>
  any make_any(Args&&... args);

Effects: Equivalent to: return any(in_place_type<T>, std::forward<Args>(args)...);

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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)...);

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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]

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template<class T>
  const T* any_cast(const any* operand) noexcept;
template<class T>
  T* any_cast(any* operand) noexcept;

Mandates: is_void_v<T> is false.

Returns: If operand != nullptr && operand->type() == typeid(T) is true, 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]