std::any:: operator=

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C++
Utilities library
General utilities
Relational operators (deprecated in C++20)
std::any
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

Run this code 
#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: 

a2.type(): "void"
cat: ""

See also

constructs an any object
(public member function)
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