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std::polymorphic<T, Allocator>::operator= - cppreference.com

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constexpr polymorphic& operator=( const polymorphic& other );

 (1) (since C++26)

constexpr polymorphic& operator=( polymorphic&& other ) noexcept(/* see below */);

 (2) (since C++26)

Replaces contents of *this with the contents of other.

Let traits be std::allocator_traits<Allocator>:

1) If std::addressof(other) == this is true, does nothing. Otherwise, let need_update be traits::propagate_on_container_copy_assignment::value:

  1. If other is valueless, proceeds to the next step. Otherwise, constructs a new owned object in *this using traits::construct with *other as the argument, using the allocator update_alloc ? other.alloc : alloc.
  2. The previously owned object in *this (if any) is destroyed using traits::destroy and then the storage is deallocated.

After updating the object owned by *this, if need_update is true, alloc is replaced with a copy of other.alloc.

2) If std::addressof(other) == this is true, does nothing. Otherwise, let need_update be traits::propagate_on_container_move_assignment::value:

  • If alloc == other.alloc is true, swaps the owned objects in *this and other; the owned object in other (if any) is then destroyed using traits::destroy and then the storage is deallocated.
  • Otherwise:
  1. If other is valueless, proceeds to the next step. Otherwise, constructs a new owned object in *this using traits::construct with std::move(*other) as the argument, using the allocator update_alloc ? other.alloc : alloc.
  2. The previously owned object in *this (if any) is destroyed using traits::destroy and then the storage is deallocated.

After updating the objects owned by *this and other, if need_update is true, alloc is replaced with a copy of other.alloc.

If all following conditions are satisfied, the program is ill-formed:

  • std::allocator_traits<Allocator>::is_always_equal::value is false.
  • T is an incomplete type.

Parameters

other - another polymorphic object whose owned value (if exists) is used for assignment

Return value

*this

Exceptions

1) If any exception is thrown, there are no effects on *this.

2) If any exception is thrown, there are no effects on *this or other.

noexcept

specification:

noexcept(std::allocator_traits<Allocator>:: propagate_on_container_move_assignment::value || std::allocator_traits<Allocator>::is_always_equal::value)

Example