std::unique_ptr<T,Deleter>::operator=
members of the primary template, unique_ptr<T> | ||
unique_ptr& operator=( unique_ptr&& r ) noexcept; |
(1) | (constexpr since C++23) |
template< class U, class E > unique_ptr& operator=( unique_ptr<U,E>&& r ) noexcept; |
(2) | (constexpr since C++23) |
unique_ptr& operator=( std::nullptr_t ) noexcept; |
(3) | (constexpr since C++23) |
members of the specialization for arrays, unique_ptr<T[]> | ||
unique_ptr& operator=( unique_ptr&& r ) noexcept; |
(1) | (constexpr since C++23) |
template< class U, class E > unique_ptr& operator=( unique_ptr<U,E>&& r ) noexcept; |
(2) | (constexpr since C++23) |
unique_ptr& operator=( std::nullptr_t ) noexcept; |
(3) | (constexpr since C++23) |
r
to
*this
as if by calling
reset(r.release())
followed by an assignment of
get_deleter()
from
std::forward<Deleter>(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 move assignment operator only participates in overload resolution if std::is_move_assignable<Deleter>::value
is true
.
- This assignment operator of the primary template only participates in overload resolution if
U
is not an array type andunique_ptr<U,E>::pointer
is implicitly convertible topointer
andstd::is_assignable<Deleter&, E&&>::value
istrue
. - 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 aselement_type*
-
unique_ptr<U,E>::pointer
is the same type asunique_ptr<U,E>::element_type*
-
unique_ptr<U,E>::element_type(*)[]
is convertible toelement_type(*)[]
-
std::is_assignable<Deleter&, E&&>::value
istrue
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 transferred |
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"; }
Output:
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.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 2118 | C++11 | unique_ptr<T[]>::operator= rejected qualification conversions |
accepts |
LWG 2228 | C++11 | the converting assignment operator was not constrained | constrained |
LWG 2899 | C++11 | the move assignment operator was not constrained | constrained |
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