67 lines
2.6 KiB
Markdown
67 lines
2.6 KiB
Markdown
[optional.iterators]
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# 22 General utilities library [[utilities]](./#utilities)
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## 22.5 Optional objects [[optional]](optional#iterators)
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### 22.5.3 Class template optional [[optional.optional]](optional.optional#optional.iterators)
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#### 22.5.3.6 Iterator support [optional.iterators]
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[ð](#lib:iterator,optional)
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`using iterator = implementation-defined;
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using const_iterator = implementation-defined;
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4059)
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These types
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model [contiguous_iterator](iterator.concept.contiguous#concept:contiguous_iterator "24.3.4.14 Concept contiguous_iterator [iterator.concept.contiguous]") ([[iterator.concept.contiguous]](iterator.concept.contiguous "24.3.4.14 Concept contiguous_iterator")),
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meet the [*Cpp17RandomAccessIterator*](random.access.iterators#:Cpp17RandomAccessIterator "24.3.5.7 Random access iterators [random.access.iterators]") requirements ([[random.access.iterators]](random.access.iterators "24.3.5.7 Random access iterators")), and
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meet the requirements for constexpr iterators ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")),
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with value type remove_cv_t<T>[.](#1.sentence-1)
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The reference type is T& for iterator andconst T& for const_iterator[.](#1.sentence-2)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4068)
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All requirements on container iterators ([[container.reqmts]](container.reqmts "23.2.2.2 Container requirements")) apply tooptional::iterator and optional::const_iterator as well[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4072)
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Any operation that initializes or destroys the contained value of an optional object invalidates all iterators into that object[.](#3.sentence-1)
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[ð](#lib:begin,optional)
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`constexpr iterator begin() noexcept;
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constexpr const_iterator begin() const noexcept;
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`
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4083)
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*Returns*: If has_value() is true,
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an iterator referring to the contained value[.](#4.sentence-1)
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Otherwise, a past-the-end iterator value[.](#4.sentence-2)
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[ð](#lib:end,optional)
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`constexpr iterator end() noexcept;
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constexpr const_iterator end() const noexcept;
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`
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L4097)
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*Returns*: begin() + has_value()[.](#5.sentence-1)
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