37 lines
2.2 KiB
Markdown
37 lines
2.2 KiB
Markdown
[bidirectional.iterators]
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# 24 Iterators library [[iterators]](./#iterators)
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## 24.3 Iterator requirements [[iterator.requirements]](iterator.requirements#bidirectional.iterators)
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### 24.3.5 C++17 iterator requirements [[iterator.cpp17]](iterator.cpp17#bidirectional.iterators)
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#### 24.3.5.6 Bidirectional iterators [bidirectional.iterators]
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2309)
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A class or pointer typeX meets the requirements of a bidirectional iterator if,
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in addition to meeting the *Cpp17ForwardIterator* requirements,
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the following expressions are valid as shown in Table [82](#tab:bidirectionaliterator "Table 82: Cpp17BidirectionalIterator requirements (in addition to Cpp17ForwardIterator)")[.](#1.sentence-1)
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Table [82](#tab:bidirectionaliterator) — *Cpp17BidirectionalIterator* requirements (in addition to *Cpp17ForwardIterator*) [[tab:bidirectionaliterator]](./tab:bidirectionaliterator)
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| [ð](#tab:bidirectionaliterator-row-1)<br>**Expression** | **Return type** | **Operational** | **Assertion/note** |
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| --- | --- | --- | --- |
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| [ð](#tab:bidirectionaliterator-row-2) | | **semantics** | **pre-/post-condition** |
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| [ð](#tab:bidirectionaliterator-row-3)<br>--r | X& | | *Preconditions*: there exists s such that r == ++s[.](#tab:bidirectionaliterator-row-3-column-4-sentence-1)<br> *Postconditions*: r is dereferenceable[.](#tab:bidirectionaliterator-row-3-column-4-sentence-2)<br> --(++r) == r[.](#tab:bidirectionaliterator-row-3-column-4-sentence-3)<br> --r == --s implies r == s[.](#tab:bidirectionaliterator-row-3-column-4-sentence-4)<br> addressof(r) == addressof(--r)[.](#tab:bidirectionaliterator-row-3-column-4-sentence-5) |
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| [ð](#tab:bidirectionaliterator-row-4)<br>r-- | convertible to const X& | { X tmp = r; --r; return tmp; } | |
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| [ð](#tab:bidirectionaliterator-row-5)<br>*r-- | reference | | |
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iterators.tex#L2342)
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[*Note [1](#note-1)*:
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Bidirectional iterators allow algorithms to move iterators backward as well as forward[.](#2.sentence-1)
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â *end note*]
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