[indirect.general]

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

## 20.4 Types for composite class design [[mem.composite.types]](mem.composite.types#indirect.general)

### 20.4.1 Class template indirect [[indirect]](indirect#general)

#### 20.4.1.1 General [indirect.general]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5901)

An indirect object manages the lifetime of an owned object[.](#1.sentence-1)

An indirect object is[*valueless*](#def:valueless,indirect_object "20.4.1.1 General [indirect.general]") if it has no owned object[.](#1.sentence-2)

An indirect object may become valueless only after it has been moved from[.](#1.sentence-3)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5907)

In every specialization indirect<T, Allocator>,
if the type allocator_traits<Allocator>​::​value_type is not the same type as T,
the program is ill-formed[.](#2.sentence-1)

Every object of type indirect<T, Allocator> uses an object of type Allocator to allocate and free storage
for the owned object as needed[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5916)

Constructing an owned object with args... using the allocator a means callingallocator_traits<Allocator>​::​construct(a, *p*, args...) whereargs is an expression pack,a is an allocator, and*p* is a pointer obtained by
calling allocator_traits<Allocator>​::​allocate[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5925)

The member *alloc* is used for
any memory allocation and element construction
performed by member functions
during the lifetime of each indirect object[.](#4.sentence-1)

The allocator *alloc* may be replaced
only via assignment or swap()[.](#4.sentence-2)

Allocator replacement is performed by
copy assignment,
move assignment, or
swapping of the allocator
only if ([[container.reqmts]](container.reqmts "23.2.2.2 Container requirements")):

- [(4.1)](#4.1)

allocator_traits<Allocator>​::​propagate_on_container_copy_assignment​::​value, or

- [(4.2)](#4.2)

allocator_traits<Allocator>​::​propagate_on_container_move_assignment​::​value, or

- [(4.3)](#4.3)

allocator_traits<Allocator>​::​propagate_on_container_swap​::​value

is true within the implementation of
the corresponding indirect operation[.](#4.sentence-3)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5948)

A program that instantiates the definition of
the template indirect<T, Allocator> with
a type for the T parameter that is
a non-object type,
an array type,in_place_t,
a specialization of in_place_type_t, or
a cv-qualified type
is ill-formed[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5959)

The template parameter T of indirect may be an incomplete type[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5963)

The template parameter Allocator of indirect shall meet the *Cpp17Allocator* requirements[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/memory.tex#L5967)

If a program declares an explicit or partial specialization of indirect,
the behavior is undefined[.](#8.sentence-1)