std::unique_ptr::operator=
From cppreference.com
< cpp | memory | unique ptr
| members of the primary template, unique_ptr<T> |
||
| unique_ptr& operator=( unique_ptr&& r ); |
(1) | |
| template< class U, class E > unique_ptr& operator=( unique_ptr<U,E>&& r ); |
(1) | |
| unique_ptr& operator=( nullptr_t ); |
(2) | |
| members of the specialization for arrays, unique_ptr<T[]> |
||
| unique_ptr& operator=( unique_ptr&& r ); |
(1) | |
| template< class U, class E > unique_ptr& operator=( unique_ptr<U,E>&& r ); |
(1) | (since C++17) |
| unique_ptr& operator=( nullptr_t ); |
(2) | |
1) Transfers ownership from
r to *this as if by calling reset(r.release()) followed by an assignment of get_deleter() from std::forward<E>(r.get_deleter()). If
Deleter is not a reference type, requires that it is nothrow-MoveAssignable. If
Deleter is a reference type, requires that std::remove_reference<Deleter>::type is nothrow-CopyAssignable. The template version of this assignment operator 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 (since C++17).|
The template version of 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
|
(since C++17) |
2) Effectively the same as calling reset().
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
| r | - | smart pointer from which ownership will be transfered |
Return value
*this
Exceptions
noexcept specification:
noexcept
Example
Run this code
#include <iostream> #include <memory> struct Foo { Foo() { std::cout << "Foo\n"; } ~Foo() { std::cout << "~Foo\n"; } }; int main() { std::unique_ptr<Foo> p1; { std::cout << "Creating new Foo...\n"; std::unique_ptr<Foo> p2(new Foo); // 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"; }
Output:
Creating new Foo... Foo About to leave inner block... About to leave program... ~Foo