std::unique_ptr<T,Deleter>::operator=

unique_ptr& operator=( unique_ptr&& r ) noexcept;

template< class U, class E >
unique_ptr& operator=( unique_ptr<U,E>&& r ) noexcept;

unique_ptr& operator=( std::nullptr_t ) noexcept;

unique_ptr& operator=( unique_ptr&& r ) noexcept;

template< class U, class E >
unique_ptr& operator=( unique_ptr<U,E>&& r ) noexcept;

unique_ptr& operator=( std::nullptr_t ) noexcept;

• This assignment operator of the primary template only participates in overload resolution if U is not an array type and unique_ptr<U,E>::pointer is implicitly convertible to pointer and std::is_assignable<Deleter&, E&&>::value is true.
• This assignment operator in the specialization for arrays, std::unique_ptr<T[]> behaves the same as in the primary template, except that will only participate in overload resolution if all of the following is true:
• U is an array type
• pointer is the same type as element_type*
• unique_ptr<U,E>::pointer is the same type as unique_ptr<U,E>::element_type*
• unique_ptr<U,E>::element_type(*)[] is convertible to element_type(*)[]
• std::is_assignable<Deleter&, E&&>::value is true

Note that unique_ptr's assignment operator only accepts rvalues, which are typically generated by std::move. (The unique_ptr class explicitly deletes its lvalue copy constructor and lvalue assignment operator.).

Parameters

Return value

*this.

Example

#include <iostream>
#include <memory>
 
struct Foo
{
    int id;
    Foo(int id) : id(id) { std::cout << "Foo " << id << '\n'; }
    ~Foo() { std::cout << "~Foo " << id << '\n'; }
};
 
int main() 
{
    std::unique_ptr<Foo> p1(std::make_unique<Foo>(1));
 
    {
        std::cout << "Creating new Foo...\n";
        std::unique_ptr<Foo> p2(std::make_unique<Foo>(2));
        // p1 = p2; // Error ! can't copy unique_ptr
        p1 = std::move(p2);
        std::cout << "About to leave inner block...\n";
 
        // Foo instance will continue to live, 
        // despite p2 going out of scope
    }
 
    std::cout << "About to leave program...\n";
}

Foo 1
Creating new Foo...
Foo 2
~Foo 1
About to leave inner block...
About to leave program...
~Foo 2

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.