MySQL 9.0.0
Source Code Documentation
visible_fields.h
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24
25#ifndef SQL_VISIBLE_FIELDS_H
26#define SQL_VISIBLE_FIELDS_H
27
28/**
29 @file
30 An adapter class to support iteration over an iterator of Item *
31 (typically mem_root_deque<Item *>), while skipping over items that
32 are hidden (item->hidden == true). This is such a common operation
33 that it warrants having its own adapter. You can either do
34
35 for (Item *item : VisibleFields(fields))
36
37 or use select->visible_fields().
38
39 Behavior is undefined if you modify the hidden flag of an item during
40 iteration.
41
42 TODO(sgunders): When we get C++20, replace with an std::views::filter.
43 */
44
45#include <iterator>
46
47#include "mem_root_deque.h"
48#include "sql/item.h"
49
50template <class Iterator>
52 public:
53 VisibleFieldsAdapter(Iterator base, Iterator end) : m_it(base), m_end(end) {
54 while (m_it != m_end && (*m_it)->hidden) {
55 ++m_it;
56 }
57 }
58
59 // Pre-increment.
61 do {
62 ++m_it;
63 } while (m_it != m_end && (*m_it)->hidden);
64 return *this;
65 }
66
67 // Post-increment.
69 VisibleFieldsAdapter ret = *this;
70 do {
71 m_it++;
72 } while (m_it != m_end && (*m_it)->hidden);
73 return ret;
74 }
75
76 auto &operator*() const { return *m_it; }
77
78 bool operator==(const VisibleFieldsAdapter &other) const {
79 return m_it == other.m_it;
80 }
81 bool operator!=(const VisibleFieldsAdapter &other) const {
82 return m_it != other.m_it;
83 }
84
85 // Define aliases needed by std::iterator_traits, to allow using this iterator
86 // type with standard library templates.
87 using difference_type = typename Iterator::difference_type;
89 using pointer = typename Iterator::pointer;
90 using reference = typename Iterator::reference;
91 using iterator_category = std::forward_iterator_tag;
92
93 private:
94 Iterator m_it, m_end;
95};
96
97template <class Container, class Iterator>
99 public:
100 explicit VisibleFieldsContainer(Container &fields) : m_fields(fields) {}
102 return VisibleFieldsAdapter<Iterator>(m_fields.begin(), m_fields.end());
103 }
106 }
107
108 private:
109 Container &m_fields;
110};
111
115}
116
117inline auto VisibleFields(const mem_root_deque<Item *> &fields) {
120}
121
122#endif // SQL_VISIBLE_FIELDS_H
Definition: visible_fields.h:51
VisibleFieldsAdapter & operator++()
Definition: visible_fields.h:60
typename Iterator::difference_type difference_type
Definition: visible_fields.h:87
Iterator m_it
Definition: visible_fields.h:94
VisibleFieldsAdapter operator++(int)
Definition: visible_fields.h:68
typename Iterator::reference reference
Definition: visible_fields.h:90
bool operator==(const VisibleFieldsAdapter &other) const
Definition: visible_fields.h:78
bool operator!=(const VisibleFieldsAdapter &other) const
Definition: visible_fields.h:81
Iterator m_end
Definition: visible_fields.h:94
typename Iterator::pointer pointer
Definition: visible_fields.h:89
VisibleFieldsAdapter(Iterator base, Iterator end)
Definition: visible_fields.h:53
std::forward_iterator_tag iterator_category
Definition: visible_fields.h:91
typename Iterator::value_type value_type
Definition: visible_fields.h:88
auto & operator*() const
Definition: visible_fields.h:76
Definition: visible_fields.h:98
VisibleFieldsContainer(Container &fields)
Definition: visible_fields.h:100
VisibleFieldsAdapter< Iterator > begin()
Definition: visible_fields.h:101
Container & m_fields
Definition: visible_fields.h:109
VisibleFieldsAdapter< Iterator > end()
Definition: visible_fields.h:104
Definition: mem_root_deque.h:288
A (partial) implementation of std::deque allocating its blocks on a MEM_ROOT.
Definition: mem_root_deque.h:111
uint16_t value_type
Definition: vt100.h:184
Cursor end()
A past-the-end Cursor.
Definition: rules_table_service.cc:192
auto VisibleFields(mem_root_deque< Item * > &fields)
Definition: visible_fields.h:112