20 General utilities library [utilities]

20.8 Storage for any type [any]

20.8.4 Non-member functions [any.nonmembers]

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

1

Effects: As if by x.swap(y).

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

2

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);

3

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

template<class ValueType> ValueType any_cast(const any& operand); template<class ValueType> ValueType any_cast(any& operand); template<class ValueType> ValueType any_cast(any&& operand);

4

Requires: is_reference_v<ValueType> is true or is_copy_constructible_v<ValueType> is true. Otherwise the program is ill-formed.

5

Returns: For the first form, *any_cast<add_const_t<remove_reference_t<ValueType>>>(&operand). For the second and third forms, *any_cast<remove_reference_t<ValueType>>(&operand).

6

Throws: bad_any_cast if operand.type() != typeid(remove_reference_t<ValueType>).

7

[ Example: 

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

8

Returns: If operand != nullptr && operand->type() == typeid(ValueType), a pointer to the object contained by operand; otherwise, nullptr.

9

[ Example: 

bool is_string(const any& operand) {
  return any_cast<string>(&operand) != nullptr;
}

 — end example ]