# std::any

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< cpp‎ | utility

Defined in header `<any>` |  |
class any; |  | (since C++17)

The class `any` describes a type-safe container for single values of any type.

1) An object of class `any` stores an instance of any type that satisfies the constructor requirements or is empty, and this is referred to as the state of the class `any` object. The stored instance is called the contained object. Two states are equivalent if they are either both empty or if both are not empty and if the contained objects are equivalent.
2) The non-member `any_cast` functions provide type-safe access to the contained object.

Implementations are encouraged to avoid dynamic allocations for small objects, but such an optimization may only be applied to types for which std::is_nothrow_move_constructible returns `true`.

### Member functions

(constructor) | constructs an `any` object (public member function)
operator= | assigns an `any` object (public member function)
(destructor) | destroys an `any` object (public member function)

##### Modifiers

emplace | change the contained object, constructing the new object directly (public member function)
reset | destroys contained object (public member function)
swap | swaps two `any` objects (public member function)

##### Observers

has_value | checks if object holds a value (public member function)
type | returns the `typeid` of the contained value (public member function)

### Non-member functions

std::swap(std::any) (C++17) | specializes the std::swap algorithm (function)
any_cast (C++17) | type-safe access to the contained object (function template)
make_any (C++17) | creates an `any` object (function template)

### Helper classes

bad_any_cast (C++17) | exception thrown by the value-returning forms of `any_cast` on a type mismatch (class)

### Example

Run this code

    #include <any>
    #include <iostream>

    int main()
    {
        std::cout << std::boolalpha;

        // any type
        std::any a = 1;
        std::cout << a.type().name() << ": " << std::any_cast<int>(a) << '\n';
        a = 3.14;
        std::cout << a.type().name() << ": " << std::any_cast<double>(a) << '\n';
        a = true;
        std::cout << a.type().name() << ": " << std::any_cast<bool>(a) << '\n';

        // bad cast
        try
        {
            a = 1;
            std::cout << std::any_cast<float>(a) << '\n';
        }
        catch (const std::bad_any_cast& e)
        {
            std::cout << e.what() << '\n';
        }

        // has value
        a = 1;
        if (a.has_value())
        {
            std::cout << a.type().name() << '\n';
        }

        // reset
        a.reset();
        if (!a.has_value())
        {
            std::cout << "no value\n";
        }

        // pointer to contained data
        a = 1;
        int* i = std::any_cast<int>(&a);
        std::cout << *i << "\n";
    }

Possible output:

    i: 1
    d: 3.14
    b: true
    bad any_cast
    i
    no value
    1

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