Difference between revisions of "cpp/named req/ReversibleContainer"
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Latest revision as of 03:22, 5 September 2024
A ReversibleContainer is a Container that has iterators that meet the requirements of either LegacyBidirectionalIterator or LegacyRandomAccessIterator. Such iterators allow a ReversibleContainer to be iterated over in reverse.
Contents |
[edit] Requirements
A type satisfies ReversibleContainer if it satisfies Container, its iterator type belongs to the bidirectional or random access iterator categories and, given the following types and values, the semantic and complexity requirements in the tables below are satisfied:
| Type | Definition |
X
|
an ReversibleContainer type |
T
|
the value_type of X
|
| Value | Definition |
| a | a value of type X
|
[edit] Types
| Name | Type | Requirements |
|---|---|---|
| typename X::reverse_iterator | std::reverse_iterator<X::iterator> | an iterator type whose value type is T
|
| typename X::const_reverse_iterator | std::reverse_iterator<X::const_iterator> | a constant iterator type whose value type is T
|
[edit] Expressions
The types reverse_iterator and const_reverse_iterator in the following table denote typename X::reverse_iterator and typename X::const_reverse_iterator respectively.
| Expression | Type | Semantics | Complexity |
|---|---|---|---|
| a.rbegin() | reverse_iteratorconst_reverse_iterator for constant a
|
reverse_iterator(a.end()) | Constant |
| a.rend() | reverse_iteratorconst_reverse_iterator for constant a
|
reverse_iterator(a.begin()) | Constant |
| a.crbegin() | const_reverse_iterator
|
const_cast<const X&>(a).rbegin() | Constant |
| a.crend() | const_reverse_iterator
|
const_cast<const X&>(a).rend() | Constant |
[edit] Standard library
- std::array
- std::deque
- std::list
- std::vector
- std::inplace_vector
- std::map
- std::multimap
- std::set
- std::multiset
[edit] Example
The following example iterates over a vector (which has random-access iterators) in reverse.
#include <iostream> #include <vector> int main() { std::vector<int> v = {3, 1, 4, 1, 5, 9}; for (std::vector<int>::const_reverse_iterator i{v.crbegin()}; i != v.crend(); ++i) std::cout << *i << ' '; std::cout << '\n'; }
Output:
9 5 1 4 1 3
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 2105 | C++98 | typename X::const_reverse_iterator was required to be an iterator type of value type const T |
required to be a constant iterator type of value type T
|
