namespace std {
class any {
public:
// [any.cons], construction and destruction
constexpr any() noexcept;
any(const any& other);
any(any&& other) noexcept;
template<class T>
any(T&& value);
template<class T, class... Args>
explicit any(in_place_type_t<T>, Args&&...);
template<class T, class U, class... Args>
explicit any(in_place_type_t<T>, initializer_list<U>, Args&&...);
~any();
// [any.assign], assignments
any& operator=(const any& rhs);
any& operator=(any&& rhs) noexcept;
template<class T>
any& operator=(T&& rhs);
// [any.modifiers], modifiers
template<class T, class... Args>
decay_t<T>& emplace(Args&&...);
template<class T, class U, class... Args>
decay_t<T>& emplace(initializer_list<U>, Args&&...);
void reset() noexcept;
void swap(any& rhs) noexcept;
// [any.observers], observers
bool has_value() const noexcept;
const type_info& type() const noexcept;
};
}

An object of class any stores an instance of any type that meets the constructor requirements or it has no value,
and this is referred to as the *state* of the class any object.

The stored instance is called the *contained value*.

Two states are equivalent if either they both have no value, or they both have a value and the contained values are equivalent.

```
constexpr any() noexcept;
```

```
any(const any& other);
```

```
any(any&& other) noexcept;
```

Otherwise, constructs an object of type any that
contains either the contained value of other, or
contains an object of the same type constructed from
the contained value of other considering that contained value as an rvalue.

```
template<class T>
any(T&& value);
```

```
template<class T, class... Args>
explicit any(in_place_type_t<T>, Args&&... args);
```

```
template<class T, class U, class... Args>
explicit any(in_place_type_t<T>, initializer_list<U> il, Args&&... args);
```

```
~any();
```

```
any& operator=(const any& rhs);
```

```
any& operator=(any&& rhs) noexcept;
```

```
template<class T>
any& operator=(T&& rhs);
```

```
template<class T, class... Args>
decay_t<T>& emplace(Args&&... args);
```

```
template<class T, class U, class... Args>
decay_t<T>& emplace(initializer_list<U> il, Args&&... args);
```

```
void reset() noexcept;
```

```
void swap(any& rhs) noexcept;
```

```
bool has_value() const noexcept;
```

```
const type_info& type() const noexcept;
```