From Jason Turner

[iterator.traits]

C++14 → C++17 2.7 KB 50 lines
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Archived: C++14 | C++17
Markdown: C++14 | C++17
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tmp/tmpz88jr3cd/{from.md → to.md} RENAMED
@@ -30,52 +30,56 @@ iterator_traits<Iterator>::reference
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  iterator_traits<Iterator>::pointer
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  ```
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  may be defined as `void`.
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- The template `iterator_traits<Iterator>` is defined as
 
 
 
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  ``` cpp
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- namespace std {
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- template<class Iterator> struct iterator_traits {
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- typedef typename Iterator::difference_type difference_type;
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- typedef typename Iterator::value_type value_type;
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- typedef typename Iterator::pointer pointer;
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- typedef typename Iterator::reference reference;
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- typedef typename Iterator::iterator_category iterator_category;
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- };
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- }
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  ```
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  It is specialized for pointers as
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  ``` cpp
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  namespace std {
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  template<class T> struct iterator_traits<T*> {
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- typedef ptrdiff_t difference_type;
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- typedef T value_type;
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- typedef T* pointer;
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- typedef T& reference;
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- typedef random_access_iterator_tag iterator_category;
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  };
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  }
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  ```
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  and for pointers to const as
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  ``` cpp
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  namespace std {
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  template<class T> struct iterator_traits<const T*> {
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- typedef ptrdiff_t difference_type;
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- typedef T value_type;
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- typedef const T* pointer;
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- typedef const T& reference;
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- typedef random_access_iterator_tag iterator_category;
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  };
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  }
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  ```
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  To implement a generic `reverse` function, a C++program can do the
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  following:
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  ``` cpp
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  template <class BidirectionalIterator>
@@ -91,5 +95,7 @@ void reverse(BidirectionalIterator first, BidirectionalIterator last) {
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  n -= 2;
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  }
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  }
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  ```
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  iterator_traits<Iterator>::pointer
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  ```
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  may be defined as `void`.
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+ If `Iterator` has valid ([[temp.deduct]]) member types
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+ `difference_type`, `value_type`, `pointer`, `reference`, and
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+ `iterator_category`, `iterator_traits<Iterator>` shall have the
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+ following as publicly accessible members:
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  ``` cpp
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+ using difference_type = typename Iterator::difference_type;
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+ using value_type = typename Iterator::value_type;
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+ using pointer = typename Iterator::pointer;
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+ using reference = typename Iterator::reference;
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+ using iterator_category = typename Iterator::iterator_category;
 
 
 
 
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  ```
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+ Otherwise, `iterator_traits<Iterator>` shall have no members by any of
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+ the above names.
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+
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  It is specialized for pointers as
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  ``` cpp
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  namespace std {
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  template<class T> struct iterator_traits<T*> {
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+ using difference_type = ptrdiff_t;
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+ using value_type = T;
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+ using pointer = T*;
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+ using reference = T&;
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+ using iterator_category = random_access_iterator_tag;
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  };
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  }
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  ```
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  and for pointers to const as
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  ``` cpp
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  namespace std {
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  template<class T> struct iterator_traits<const T*> {
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+ using difference_type = ptrdiff_t;
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+ using value_type = T;
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+ using pointer = const T*;
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+ using reference = const T&;
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+ using iterator_category = random_access_iterator_tag;
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  };
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  }
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  ```
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+ [*Example 1*:
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+
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  To implement a generic `reverse` function, a C++program can do the
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  following:
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  ``` cpp
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  template <class BidirectionalIterator>
 
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  n -= 2;
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  }
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  }
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  ```
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+ — *end example*]
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+