Difference between revisions of "cpp/named req/Iterator"
m (→Defect reports: r) |
(→Requirements: +type of *it) |
||
| Line 15: | Line 15: | ||
* [[cpp/language/value_category|lvalues]] of type {{c|It}} satisfy {{named req|Swappable}}, and | * [[cpp/language/value_category|lvalues]] of type {{c|It}} satisfy {{named req|Swappable}}, and | ||
* {{c|std::iterator_traits<It>}} has member typedefs {{rev inl|until=c++20|{{tt|value_type}}}}, {{tt|difference_type}}, {{tt|reference}}, {{tt|pointer}}, and {{tt|iterator_category}} {{mark unreviewed dr|LWG|2578}}, and | * {{c|std::iterator_traits<It>}} has member typedefs {{rev inl|until=c++20|{{tt|value_type}}}}, {{tt|difference_type}}, {{tt|reference}}, {{tt|pointer}}, and {{tt|iterator_category}} {{mark unreviewed dr|LWG|2578}}, and | ||
| − | * Given {{c| | + | * Given {{c|it_lvalue}}, an lvalue of type {{c|It}}, the following expressions must be valid and have their specified effects: |
{|table class=wikitable | {|table class=wikitable | ||
| Line 21: | Line 21: | ||
!Expression||Return Type||Precondition | !Expression||Return Type||Precondition | ||
|- | |- | ||
| − | |{{c|* | + | |{{c|*it_lvalue}} |
| − | | | + | |{{c|std::iterator_traits<It>::reference}} |
| − | |{{c| | + | |{{c|it_lvalue}} is [[cpp/iterator#Dereferenceability and validity|dereferenceable]] |
|- | |- | ||
| − | |{{c|++ | + | |{{c|++it_lvalue}} |
|{{c|It&}} | |{{c|It&}} | ||
| − | |{{c| | + | |{{c|it_lvalue}} is ''incrementable'' (the behavior of the expression {{c|++it_lvalue}} is defined) |
|} | |} | ||
Revision as of 02:33, 17 July 2024
The LegacyIterator requirements describe types that can be used to identify and traverse the elements of a container.
LegacyIterator is the base set of requirements used by other iterator types: LegacyInputIterator, LegacyOutputIterator, LegacyForwardIterator, LegacyBidirectionalIterator, and LegacyRandomAccessIterator. Iterators can be thought of as an abstraction of pointers.
All the categories of iterators require only those functions that are realizable for a given category in constant time (amortized). Therefore, requirement tables and concept definitions (since C++20)for the iterators do not specify complexity.
Contents |
Requirements
The type It satisfies LegacyIterator if
- The type It satisfies CopyConstructible, and
- The type It satisfies CopyAssignable, and
- The type It satisfies Destructible, and
- lvalues of type It satisfy Swappable, and
- std::iterator_traits<It> has member typedefs
value_type(until C++20),difference_type,reference,pointer, anditerator_category, and - Given it_lvalue, an lvalue of type It, the following expressions must be valid and have their specified effects:
| Expression | Return Type | Precondition |
|---|---|---|
| *it_lvalue | std::iterator_traits<It>::reference | it_lvalue is dereferenceable |
| ++it_lvalue | It& | it_lvalue is incrementable (the behavior of the expression ++it_lvalue is defined) |
ConceptFor the definition of std::iterator_traits, the following exposition-only concept is defined.
where the exposition-only concept __Referenceable<T> is satisfied if and only if T& is a valid type (in particular, T must not be void). |
(since C++20) |
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 3420 | C++20 | the exposition-only concept checks copyable first
|
copyable is checked only if the requires-expression yields true
|
See also
| (C++20) |
specifies that objects of a type can be incremented and dereferenced (concept) |
| Iterator library | provides definitions for iterators, iterator traits, adaptors, and utility functions |
