[polymorphic.assign]

# 20 Memory management library [[mem]](./#mem)

## 20.4 Types for composite class design [[mem.composite.types]](mem.composite.types#polymorphic.assign)

### 20.4.2 Class template polymorphic [[polymorphic]](polymorphic#assign)

#### 20.4.2.5 Assignment [polymorphic.assign]

[🔗](#lib:operator=,polymorphic)

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

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7236)

*Mandates*: T is a complete type[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7240)

*Effects*: If addressof(other) == this is true, there are no effects[.](#2.sentence-1)

Otherwise:

- [(2.1)](#2.1)

  The allocator needs updating ifallocator_traits<Allocator>​::​propagate_on_container_copy_assignment​::​value is true[.](#2.1.sentence-1)

- [(2.2)](#2.2)

  If other is not valueless,
a new owned object is constructed in *this usingallocator_traits<Allocator>​::​construct with
the owned object from other as the argument, using either
the allocator in *this or
the allocator in other if the allocator needs updating[.](#2.2.sentence-1)

- [(2.3)](#2.3)

  The previously owned object in *this, if any,
is destroyed using allocator_traits<Allocator>​::​  
destroy and
then the storage is deallocated[.](#2.3.sentence-1)

- [(2.4)](#2.4)

  If the allocator needs updating,
the allocator in *this is replaced with
a copy of the allocator in other[.](#2.4.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7272)

*Returns*: A reference to *this[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7276)

*Remarks*: If any exception is thrown, there are no effects on *this[.](#4.sentence-1)

[🔗](#lib:operator=,polymorphic_)

`constexpr polymorphic& operator=(polymorphic&& other)
  noexcept(allocator_traits<Allocator>::propagate_on_container_move_assignment::value ||
           allocator_traits<Allocator>::is_always_equal::value);
`

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7289)

*Mandates*: If allocator_traits<Allocator>​::​is_always_equal​::​value is false,T is a complete type[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7294)

*Effects*: If addressof(other) == this is true, there are no effects[.](#6.sentence-1)

Otherwise:

- [(6.1)](#6.1)

  The allocator needs updating ifallocator_traits<Allocator>​::​propagate_on_container_move_assignment​::​value is true[.](#6.1.sentence-1)

- [(6.2)](#6.2)

  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 allocator_traits<Allocator>​::​destroy and
then the storage is deallocated[.](#6.2.sentence-1)

- [(6.3)](#6.3)

  Otherwise,
if *alloc* != other.*alloc* is true;
if other is not valueless,
a new owned object is constructed in *this using allocator_traits<Allocator>​::​construct with
the owned object from other as the argument as an rvalue,
using either the allocator in *this or
the allocator in other if the allocator needs updating[.](#6.3.sentence-1)

- [(6.4)](#6.4)

  The previously owned object in *this, if any,
is destroyed using allocator_traits<Allocator>​::​  
destroy and
then the storage is deallocated[.](#6.4.sentence-1)

- [(6.5)](#6.5)

  If the allocator needs updating,
the allocator in *this is replaced with
a copy of the allocator in other[.](#6.5.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7336)

*Returns*: A reference to *this[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L7340)

*Remarks*: If any exception is thrown,
there are no effects on *this or other[.](#8.sentence-1)