Category: containers
Component type: concept
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.
None, except for those of Sequence.
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 |
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 |
| 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. |
Back, push back, and pop back are amortized constant time. [1]
| Symmetry of push and pop | push_back() followed by pop_back() is a null operation. |
[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.
1.7.3
