C++ concepts: AllocatorAwareContainer
From cppreference.com
An AllocatorAwareContainer is a Container that holds an instance of an Allocator and uses that instance to allocate and deallocate memory in all of its member functions.
The following rules apply to object construction
- Copy constructors of
AllocatorAwareContainers obtain their instances of the allocator by calling std::allocator_traits<allocator_type>::select_on_container_copy_construction on the allocator of the container being copied. - Move constructors obtain their instances of allocators by move-constructing from the allocator belonging to the old container.
- All other constructors take an allocator parameter.
The only way to replace an allocator is copy-assignment, move-assignment, and swap:
- Copy-assignment will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_copy_assignment::value is true
- Move-assignment will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_move_assignment::value is true
- Swap will replace the allocator only if std::allocator_traits<allocator_type>::propagate_on_container_swap::value is true. Specifically, it will exchange the allocator instances through an unqualified call to the non-member function swap, see
Swappable.
Note: swapping two containers with unequal allocators if propagate_on_container_swap is false is undefined behavior.
- The accessor
get_allocator()obtains a copy of the allocator that was used to construct the container or installed by the most recent allocator replacement operation.
Contents |
[edit] Requirements
Legend | |
X
|
Container type |
T
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Element type |
A
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Allocator for T
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a, b
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Objects of type X (non-const lvalue)
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t
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Object of type X (lvalue or const rvalue)
|
rv
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Object of type X (non-const rvalue)
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m
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Object of type A
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Q
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Allocator type |
| expression | return type | pre/requirements | post/effects | complexity |
|---|---|---|---|---|
| allocator_type | A |
allocator_type::value_type must be the same as X::value_type | constant | |
| get_allocator() | A |
constant | ||
| X u; | A is DefaultConstructible |
u.empty() == true && u.get_allocator() == A() | constant | |
| X u(m); | u.empty() == true && u.get_allocator() == m | constant | ||
| X u(t,m); | T is CopyInsertable into X
|
u == t && u.get_allocator() == m | linear | |
| X u(rv); | Move constructor of A must not throw exceptions
|
u has the same elements and an equal allocator as rv had before the construction |
constant | |
| X u(rv,m); | T is MoveInsertable into X
|
The elements of u are the same or copies of those of rv and u.get_allocator() == m
|
constant if m == rv.get_allocator(), otherwise linear | |
| a = t | X& | T is CopyInsertable into X and CopyAssignable |
a == t | linear |
| a = rv | X& | If the allocator will not be replaced by move-assignment (see above), then T is MoveInsertable into X and MoveAssignable
|
All existing elements of a are either move assigned to or destroyed; a is equal to the value that rv had before the assignment |
linear |
| a.swap(b) | void | Exchanges the contents of a and b |
constant |
[edit] Concept requirements
- A
- T
- X
[edit] Standard library
All standard library containers except std::array are AllocatorAwareContainers:
