Книга: Standard Template Library Programmer
Back Insertion Sequence
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Back Insertion Sequence
Category: containers
Component type: concept
Description
A Back Insertion Sequence is a Sequence where it is possible to append an element to the end, or to access the last element, in amortized constant time. Back Insertion Sequences have special member functions as a shorthand for those operations.
Refinement of
Sequence
Associated types
None, except for those of Sequence.
Notation
X A type that is a model of Back Insertion Sequence
a Object of type X
T The value type of X
t Object of type T
Valid expressions
In addition to the expressions defined in Sequence, the following expressions must be valid.
| Name | Expression | Type requirements | Return type |
|---|---|---|---|
| Back | a.back() |
reference if a is mutable, otherwise const_reference. | |
| Push back | a.push_back(t) |
a is mutable. | void |
| Pop back | a.pop_back() |
a is mutable. | void |
Expression semantics
| Name | Expression | Precondition | Semantics | Postcondition |
|---|---|---|---|---|
| Back | a.back() |
!a.empty() |
Equivalent to *(--a.end()). | |
| Push back | a.push_back(t) |
Equivalent to a.insert(a.end(), t) a.size is incremented by 1. | a.back() is a copy of t. | |
| Pop back | a.pop_back() |
!a.empty() |
Equivalent to a.erase(--a.end()) | a.size() is decremented by 1. |
Complexity guarantees
Back, push back, and pop back are amortized constant time. [1]
Invariants
| Symmetry of push and pop | push_back() followed by pop_back() is a null operation. |
Models
vector
list
deque
Notes
[1] This complexity guarantee is the only reason that back(), push_back(), and pop_back() are defined: they provide no additional functionality. Not every sequence must define these operations, but it is guaranteed that they are efficient if they exist at all.
See also
Container, Sequence, Front Insertion Sequence, vector, deque, list
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