C++ named requirements: LegacyBidirectionalIterator - cppreference.com (original) (raw)
A LegacyBidirectionalIterator is a LegacyForwardIterator that can be moved in both directions (i.e. incremented and decremented).
If a LegacyBidirectionalIterator it originates from a Container, then it's value_type is the same as the container's, so dereferencing (*it) obtains the container's value_type.
[edit] Requirements
The type It satisfies LegacyBidirectionalIterator if
- The type
Itsatisfies LegacyForwardIterator
And, given
- a and b, lvalues of type
It reference, the type denoted by std::iterator_traits<It>::reference
The following expressions must be valid and have their specified effects:
| Expression | Return | Equivalent expression | Notes |
|---|---|---|---|
| --a | It& | Preconditions: a is decrementable (there exists such b that a == ++b) Postconditions: a is dereferenceable --(++a) == a If --a == --b then a == b a and --a designate the same iterator object | |
| a-- | convertible to const It& | It temp = a; --a; return temp; | |
| *a-- | reference |
A mutable LegacyBidirectionalIterator is a LegacyBidirectionalIterator that additionally satisfies the LegacyOutputIterator requirements.
[edit] Notes
The begin iterator is not decrementable and the behavior is undefined if --container.begin() is evaluated.
A bidirectional iterator does not have to be dereferenceable to be decrementable (in particular, the end iterator is not dereferenceable but is decrementable).
| Concept For the definition of std::iterator_traits, the following exposition-only concept is defined. where the exposition-only concept __LegacyForwardIterator is described in LegacyForwardIterator. | (since C++20) |
|---|
[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 299(N3066) | C++98 | the return type of *a-- wasrequired to be convertible to T | changed the returntype to reference[1] |
| LWG 383 | C++98 | b was required to be dereferenceable after --a | a is required to be dereferenceable instead |
| LWG 1212(N3066) | C++98 | the return type of *a-- did not match the returntype of *a++ required by LegacyForwardIterator | changed the returntype to reference |
- ↑ This issue was initially resolved by N2758 (iterator concepts), which was dropped later from the C++ standard.