std::any::operator=

any& operator=( const any& rhs );	(1)	(since C++17)
any& operator=( any&& rhs ) noexcept;	(2)	(since C++17)
template< typename ValueType > any& operator=( ValueType&& rhs );	(3)	(since C++17)

Assigns contents to the contained value.

1) Assigns by copying the state of rhs, as if by std::any(rhs).swap(*this).

2) Assigns by moving the state of rhs, as if by std::any(std::move(rhs)).swap(*this). rhs is left in a valid but unspecified state after the assignment.

3) Assigns the type and value of rhs, as if by std::any(std::forward<ValueType>(rhs)).swap(*this). This overload participates in overload resolution only if std::decay_t<ValueType> is not the same type as std::any and std::is_copy_constructible_v<std::decay_t<ValueType>> is true.

Template parameters

ValueType	-	contained value type
Type requirements
-`std::decay_t<ValueType>` must meet the requirements of CopyConstructible.

Parameters

rhs

object whose contained value to assign

Return value

*this

Exceptions

1,3) Throws std::bad_alloc or any exception thrown by the constructor of the contained type. If an exception is thrown for any reason, these functions have no effect (strong exception safety guarantee).

Example

#include <any>
#include <cassert>
#include <iomanip>
#include <iostream>
#include <string>
#include <typeinfo>

int main()
{
    using namespace std::string_literals;
    std::string cat{"cat"};

    std::any a1{42};
    std::any a2{cat};
    assert(a1.type() == typeid(int));
    assert(a2.type() == typeid(std::string));

    a1 = a2; // overload (1)
    assert(a1.type() == typeid(std::string));
    assert(a2.type() == typeid(std::string));
    assert(std::any_cast<std::string&>(a1) == cat);
    assert(std::any_cast<std::string&>(a2) == cat);

    a1 = 96; // overload (3)
    a2 = "dog"s; // overload (3)
    a1 = std::move(a2); // overload (2)
    assert(a1.type() == typeid(std::string));
    assert(std::any_cast<std::string&>(a1) == "dog");
    // The state of a2 is valid but unspecified. In fact,
    // it is void in gcc/clang and std::string in msvc.
    std::cout << "a2.type(): " << std::quoted(a2.type().name()) << '\n';

    a1 = std::move(cat); // overload (3)
    assert(*std::any_cast<std::string>(&a1) == "cat");
    // The state of cat is valid but indeterminate:
    std::cout << "cat: " << std::quoted(cat) << '\n';
}

Possible output: