sql_list.h

Go to the documentation of this file.

#ifndef INCLUDES_MYSQL_SQL_LIST_H
#define INCLUDES_MYSQL_SQL_LIST_H
/* Copyright (c) 2000, 2025, Oracle and/or its affiliates.
 
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License, version 2.0,
   as published by the Free Software Foundation.
 
   This program is designed to work with certain software (including
   but not limited to OpenSSL) that is licensed under separate terms,
   as designated in a particular file or component or in included license
   documentation.  The authors of MySQL hereby grant you an additional
   permission to link the program and your derivative works with the
   separately licensed software that they have either included with
   the program or referenced in the documentation.
 
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License, version 2.0, for more details.
 
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */
 
#include <stddef.h>
#include <sys/types.h>
#include <algorithm>
#include <iterator>
#include <memory>
#include <type_traits>
#include <utility>
 
#include "my_alloc.h"
#include "my_compiler.h"
#include "my_dbug.h"
#include "my_sharedlib.h"
#include "sql/thr_malloc.h"
 
/**
  Simple intrusive linked list.
 
  @remark Similar in nature to base_list, but intrusive. It keeps a
          a pointer to the first element in the list and a indirect
          reference to the last element.
*/
template <typename T>
class SQL_I_List {
 public:
  uint elements;
  /** The first element in the list. If empty, nullptr */
  T *first;
  /**
    A reference to the next element in the list. If empty points to
    the head element's 'first' pointer, else to the last element's
    next pointer.
  */
  T **next;
 
  SQL_I_List() { clear(); }
 
  SQL_I_List(const SQL_I_List &tmp)
      : elements(tmp.elements),
        first(tmp.first),
        next(elements ? tmp.next : &first) {}
 
  SQL_I_List(SQL_I_List &&that)
      : elements(that.elements),
        first(that.first),
        next((elements != 0) ? that.next : &first) {
    that.clear();
  }
 
  inline void clear() {
    elements = 0;
    first = nullptr;
    next = &first;
  }
 
  inline void link_in_list(T *element, T **next_ptr) {
    elements++;
    (*next) = element;
    next = next_ptr;
    *next = nullptr;
  }
 
  inline void save_and_clear(SQL_I_List<T> *save) { *save = std::move(*this); }
 
  inline void push_front(SQL_I_List<T> *save) {
    /* link current list last */
    *save->next = first;
    first = save->first;
    elements += save->elements;
  }
 
  inline void push_back(SQL_I_List<T> *save) {
    if (save->first) {
      *next = save->first;
      next = save->next;
      elements += save->elements;
    }
  }
 
  /*
    Split list after sz elements into two: this list gets shortened, the rest
    gets assigned into tail.  If sz is larger than or equal to the number of
    elements in this list, this list is unchanged, and tail will be empty
 
    @param sz   The number of elements to retain in this list
    @param tail The list to hold the tail we chop off.
  */
  void split_after(uint sz, SQL_I_List<T> *tail) {
    assert(this != tail);
    if (sz >= elements) {  // just put an empty list in tail
      *tail = std::move(SQL_I_List<T>());
      return;
    }
    T **o = &first;
    for (uint i = 0; i < sz; i++) {
      o = &(*o)->next;
    }
    // Save tail
    tail->first = *o;
    tail->next = next;
    tail->elements = elements - sz;
    // Shorten this
    next = o;
    *next = nullptr;
    elements = sz;
  }
 
  inline uint size() const { return elements; }
 
  SQL_I_List &operator=(SQL_I_List &that) {
    if (this == &that) {
      return *this;
    }
    elements = that.elements;
    first = that.first;
    next = (elements != 0) ? that.next : &first;
    return *this;
  }
 
  SQL_I_List &operator=(SQL_I_List &&that) {
    if (this == &that) {
      return *this;
    }
    elements = that.elements;
    first = that.first;
    next = (elements != 0) ? that.next : &first;
    that.clear();
    return *this;
  }
};
 
/*
  Basic single linked list
  Used for item and item_buffs.
  All list ends with a pointer to the 'end_of_list' element, which
  data pointer is a null pointer and the next pointer points to itself.
  This makes it very fast to traverse lists as we don't have to
  test for a specialend condition for list that can't contain a null
  pointer.
*/
 
/**
  list_node - a node of a single-linked list.
  @note We never call a destructor for instances of this class.
*/
 
struct list_node {
  list_node *next;
  void *info;
  list_node(void *info_par, list_node *next_par)
      : next(next_par), info(info_par) {}
  list_node() /* For end_of_list */
  {
    info = nullptr;
    next = this;
  }
};
 
extern MYSQL_PLUGIN_IMPORT list_node end_of_list;
 
class base_list {
 protected:
  list_node *first, **last;
 
 public:
  uint elements;
 
  bool operator==(const base_list &rhs) const {
    return elements == rhs.elements && first == rhs.first && last == rhs.last;
  }
 
  inline void clear() {
    elements = 0;
    first = &end_of_list;
    last = &first;
  }
  inline base_list() { clear(); }
  /**
    This is a shallow copy constructor that implicitly passes the ownership
    from the source list to the new instance. The old instance is not
    updated, so both objects end up sharing the same nodes. If one of
    the instances then adds or removes a node, the other becomes out of
    sync ('last' pointer), while still operational. Some old code uses and
    relies on this behaviour. This logic is quite tricky: please do not use
    it in any new code.
  */
  base_list(const base_list &tmp)
      : first(tmp.first),
        last(tmp.elements ? tmp.last : &first),
        elements(tmp.elements) {}
  base_list &operator=(const base_list &tmp) {
    elements = tmp.elements;
    first = tmp.first;
    last = elements ? tmp.last : &first;
    return *this;
  }
  /**
    Construct a deep copy of the argument in memory root mem_root.
    The elements themselves are copied by pointer.
  */
  base_list(const base_list &rhs, MEM_ROOT *mem_root);
  inline bool push_back(void *info) {
    *last = new (*THR_MALLOC) list_node(info, &end_of_list);
    if (*last) {
      last = &(*last)->next;
      elements++;
      return false;
    }
    return true;
  }
  inline bool push_back(void *info, MEM_ROOT *mem_root) {
    *last = new (mem_root) list_node(info, &end_of_list);
    if (*last) {
      last = &(*last)->next;
      elements++;
      return false;
    }
    return true;
  }
  inline bool push_front(void *info) {
    list_node *node = new (*THR_MALLOC) list_node(info, first);
    if (node) {
      if (last == &first) last = &node->next;
      first = node;
      elements++;
      return false;
    }
    return true;
  }
  inline bool push_front(void *info, MEM_ROOT *mem_root) {
    list_node *node = new (mem_root) list_node(info, first);
    if (node) {
      if (last == &first) last = &node->next;
      first = node;
      elements++;
      return false;
    }
    return true;
  }
 
  void remove(list_node **prev) {
    list_node *node = (*prev)->next;
    if (!--elements)
      last = &first;
    else if (last == &(*prev)->next)
      last = prev;
    ::destroy_at(*prev);
    *prev = node;
  }
  inline void concat(base_list *list) {
    if (!list->is_empty()) {
      *last = list->first;
      last = list->last;
      elements += list->elements;
    }
  }
  inline void *pop(void) {
    if (first == &end_of_list) return nullptr;
    list_node *tmp = first;
    first = first->next;
    if (!--elements) last = &first;
    return tmp->info;
  }
  inline void disjoin(base_list *list) {
    list_node **prev = &first;
    list_node *node = first;
    list_node *list_first = list->first;
    elements = 0;
    while (node && node != list_first) {
      prev = &node->next;
      node = node->next;
      elements++;
    }
    *prev = *last;
    last = prev;
  }
  inline void prepend(base_list *list) {
    if (!list->is_empty()) {
      *list->last = first;
      if (is_empty()) last = list->last;
      first = list->first;
      elements += list->elements;
    }
  }
  /**
    Swap two lists.
  */
  inline void swap(base_list &rhs) {
    std::swap(first, rhs.first);
    std::swap(last, rhs.last);
    std::swap(elements, rhs.elements);
  }
  inline list_node *last_node() { return *last; }
  inline list_node *first_node() { return first; }
  inline void *head() { return first->info; }
  inline const void *head() const { return first->info; }
  inline void **head_ref() {
    return first != &end_of_list ? &first->info : nullptr;
  }
  inline bool is_empty() const { return first == &end_of_list; }
  inline list_node *last_ref() { return &end_of_list; }
  inline uint size() const { return elements; }
  friend class base_list_iterator;
  friend class error_list;
  friend class error_list_iterator;
 
#ifdef LIST_EXTRA_DEBUG
  /*
    Check list invariants and print results into trace. Invariants are:
      - (*last) points to end_of_list
      - There are no NULLs in the list.
      - base_list::elements is the number of elements in the list.
 
    SYNOPSIS
      check_list()
        name  Name to print to trace file
 
    RETURN
      1  The list is Ok.
      0  List invariants are not met.
  */
 
  bool check_list(const char *name) {
    base_list *list = this;
    list_node *node = first;
    uint cnt = 0;
 
    while (node->next != &end_of_list) {
      if (!node->info) {
        DBUG_PRINT("list_invariants",
                   ("%s: error: NULL element in the list", name));
        return false;
      }
      node = node->next;
      cnt++;
    }
    if (last != &(node->next)) {
      DBUG_PRINT("list_invariants", ("%s: error: wrong last pointer", name));
      return false;
    }
    if (cnt + 1 != elements) {
      DBUG_PRINT("list_invariants", ("%s: error: wrong element count", name));
      return false;
    }
    DBUG_PRINT("list_invariants", ("%s: list is ok", name));
    return true;
  }
#endif  // LIST_EXTRA_DEBUG
 
 protected:
  void after(void *info, list_node *node) {
    list_node *new_node = new (*THR_MALLOC) list_node(info, node->next);
    node->next = new_node;
    elements++;
    if (last == &(node->next)) last = &new_node->next;
  }
  bool after(void *info, list_node *node, MEM_ROOT *mem_root) {
    list_node *new_node = new (mem_root) list_node(info, node->next);
    if (!new_node) return true;  // OOM
 
    node->next = new_node;
    elements++;
    if (last == &(node->next)) last = &new_node->next;
 
    return false;
  }
#ifndef NDEBUG
 private:
  /// For debugging purposes (e.g. forced call from gdb). Return a pointer to
  /// element number 'index', or nullptr if 'index' >= 'elements'.
  void *at(uint index);
#endif
};
 
class base_list_iterator {
 protected:
  base_list *list;
  list_node **el, **prev, *current;
  void sublist(base_list &ls, uint elm) {
    ls.first = *el;
    ls.last = list->last;
    ls.elements = elm;
  }
 
 public:
  base_list_iterator()
      : list(nullptr), el(nullptr), prev(nullptr), current(nullptr) {}
 
  base_list_iterator(base_list &list_par) { init(list_par); }
 
  inline void init(base_list &list_par) {
    list = &list_par;
    el = &list_par.first;
    prev = nullptr;
    current = nullptr;
  }
 
  inline void *next(void) {
    prev = el;
    current = *el;
    el = &current->next;
    return current->info;
  }
  inline void *next_fast(void) {
    list_node *tmp;
    tmp = *el;
    el = &tmp->next;
    return tmp->info;
  }
  inline void rewind(void) { el = &list->first; }
  inline void *replace(void *element) {  // Return old element
    void *tmp = current->info;
    assert(current->info != nullptr);
    current->info = element;
    return tmp;
  }
  void *replace(base_list &new_list) {
    void *ret_value = current->info;
    if (!new_list.is_empty()) {
      *new_list.last = current->next;
      current->info = new_list.first->info;
      current->next = new_list.first->next;
      if ((list->last == &current->next) && (new_list.elements > 1))
        list->last = new_list.last;
      list->elements += new_list.elements - 1;
    }
    return ret_value;  // return old element
  }
  inline void remove(void)  // Remove current
  {
    list->remove(prev);
    el = prev;
    current = nullptr;  // Safeguard
  }
  void after(void *element)  // Insert element after current
  {
    list->after(element, current);
    current = current->next;
    el = &current->next;
  }
  bool after(void *a, MEM_ROOT *mem_root) {
    if (list->after(a, current, mem_root)) return true;
 
    current = current->next;
    el = &current->next;
    return false;
  }
  inline void **ref(void)  // Get reference pointer
  {
    return &current->info;
  }
  inline bool is_last(void) { return el == list->last; }
  inline bool is_before_first() const { return current == nullptr; }
  bool prepend(void *a, MEM_ROOT *mem_root) {
    if (list->push_front(a, mem_root)) return true;
 
    el = &list->first;
    prev = el;
    el = &(*el)->next;
 
    return false;
  }
  friend class error_list_iterator;
};
 
template <class T>
class List_STL_Iterator;
 
template <class T>
class List : public base_list {
 public:
  List() : base_list() {}
  inline List(const List<T> &tmp) : base_list(tmp) {}
  List &operator=(const List &tmp) {
    return static_cast<List &>(base_list::operator=(tmp));
  }
  inline List(const List<T> &tmp, MEM_ROOT *mem_root)
      : base_list(tmp, mem_root) {}
  /*
    Typecasting to (void *) it's necessary if we want to declare List<T> with
    constant T parameter (like List<const char>), since the untyped storage
    is "void *", and assignment of const pointer to "void *" is a syntax error.
  */
  inline bool push_back(T *a) {
    return base_list::push_back(const_cast<void *>(((const void *)a)));
  }
  inline bool push_back(T *a, MEM_ROOT *mem_root) {
    return base_list::push_back(const_cast<void *>((const void *)a), mem_root);
  }
  inline bool push_front(T *a) {
    return base_list::push_front(const_cast<void *>((const void *)a));
  }
  inline bool push_front(T *a, MEM_ROOT *mem_root) {
    return base_list::push_front(const_cast<void *>((const void *)a), mem_root);
  }
  inline T *head() { return static_cast<T *>(base_list::head()); }
  inline const T *head() const {
    return static_cast<const T *>(base_list::head());
  }
  inline T **head_ref() { return (T **)base_list::head_ref(); }
  inline T *pop() { return (T *)base_list::pop(); }
  inline void concat(List<T> *list) { base_list::concat(list); }
  inline void disjoin(List<T> *list) { base_list::disjoin(list); }
  inline void prepend(List<T> *list) { base_list::prepend(list); }
  void delete_elements(void) {
    list_node *element, *next;
    for (element = first; element != &end_of_list; element = next) {
      next = element->next;
      delete (T *)element->info;
    }
    clear();
  }
 
  void destroy_elements(void) {
    list_node *element, *next;
    for (element = first; element != &end_of_list; element = next) {
      next = element->next;
      ::destroy_at((T *)element->info);
    }
    clear();
  }
 
  T *operator[](uint index) const {
    assert(index < elements);
    list_node *current = first;
    for (uint i = 0; i < index; ++i) current = current->next;
    return static_cast<T *>(current->info);
  }
 
  void replace(uint index, T *new_value) {
    assert(index < elements);
    list_node *current = first;
    for (uint i = 0; i < index; ++i) current = current->next;
    current->info = new_value;
  }
 
  bool swap_elts(uint index1, uint index2) {
    if (index1 == index2) return false;
 
    if (index1 >= elements || index2 >= elements) return true;  // error
 
    if (index2 < index1) std::swap(index1, index2);
 
    list_node *current1 = first;
    for (uint i = 0; i < index1; ++i) current1 = current1->next;
 
    list_node *current2 = current1;
    for (uint i = 0; i < index2 - index1; ++i) current2 = current2->next;
 
    std::swap(current1->info, current2->info);
 
    return false;
  }
 
  /**
    @brief
    Sort the list
 
    @param cmp  node comparison function
 
    @details
    The function sorts list nodes by an exchange sort algorithm.
    The order of list nodes isn't changed, values of info fields are
    swapped instead. Due to this, list iterators that are initialized before
    sort could be safely used after sort, i.e they wouldn't cause a crash.
    As this isn't an effective algorithm the list to be sorted is supposed to
    be short.
  */
  template <typename Node_cmp_func>
  void sort(Node_cmp_func cmp) {
    if (elements < 2) return;
    for (list_node *n1 = first; n1 && n1 != &end_of_list; n1 = n1->next) {
      for (list_node *n2 = n1->next; n2 && n2 != &end_of_list; n2 = n2->next) {
        if (cmp(static_cast<T *>(n1->info), static_cast<T *>(n2->info)) > 0) {
          void *tmp = n1->info;
          n1->info = n2->info;
          n2->info = tmp;
        }
      }
    }
  }
 
  // For C++11 range-based for loops.
  using iterator = List_STL_Iterator<T>;
  iterator begin() { return iterator(first); }
  iterator end() {
    // If the list overlaps another list, last isn't actually
    // the last element, and if so, we'd give a different result from
    // List_iterator_fast.
    assert((*last)->next == &end_of_list);
 
    return iterator(*last);
  }
 
  using const_iterator = List_STL_Iterator<const T>;
  const_iterator begin() const { return const_iterator(first); }
  const_iterator end() const {
    assert((*last)->next == &end_of_list);
    return const_iterator(*last);
  }
  const_iterator cbegin() const { return const_iterator(first); }
  const_iterator cend() const {
    assert((*last)->next == &end_of_list);
    return const_iterator(*last);
  }
};
 
template <class T>
class List_iterator : public base_list_iterator {
 public:
  List_iterator(List<T> &a) : base_list_iterator(a) {}
  List_iterator() : base_list_iterator() {}
  inline void init(List<T> &a) { base_list_iterator::init(a); }
  inline T *operator++(int) { return (T *)base_list_iterator::next(); }
  inline T *replace(T *a) { return (T *)base_list_iterator::replace(a); }
  inline T *replace(List<T> &a) { return (T *)base_list_iterator::replace(a); }
  inline void rewind(void) { base_list_iterator::rewind(); }
  inline void remove() { base_list_iterator::remove(); }
  inline void after(T *a) { base_list_iterator::after(a); }
  inline bool after(T *a, MEM_ROOT *mem_root) {
    return base_list_iterator::after(a, mem_root);
  }
  inline T **ref(void) {
    return const_cast<T **>(
        (std::remove_const_t<T> **)base_list_iterator::ref());
  }
};
 
template <class T>
class List_iterator_fast : public base_list_iterator {
 protected:
  inline T *replace(T *) { return (T *)0; }
  inline T *replace(List<T> &) { return (T *)0; }
  inline void remove(void) {}
  inline void after(T *) {}
  inline T **ref(void) { return (T **)0; }
 
 public:
  inline List_iterator_fast(List<T> &a) : base_list_iterator(a) {}
  inline List_iterator_fast() : base_list_iterator() {}
  inline void init(List<T> &a) { base_list_iterator::init(a); }
  inline T *operator++(int) { return (T *)base_list_iterator::next_fast(); }
  inline void rewind(void) { base_list_iterator::rewind(); }
  void sublist(List<T> &list_arg, uint el_arg) {
    base_list_iterator::sublist(list_arg, el_arg);
  }
};
 
/*
  Like List_iterator<T>, but with an STL-compatible interface
  (ForwardIterator), so that you can use it in range-based for loops.
  Prefer this to List_iterator<T> wherever possible, but also prefer
  std::vector<T> or std::list<T> to List<T> wherever possible.
 */
template <class T>
class List_STL_Iterator {
 public:
  explicit List_STL_Iterator(list_node *node) : m_current(node) {}
 
  // Iterator (required for InputIterator).
  T &operator*() const { return *static_cast<T *>(m_current->info); }
 
  List_STL_Iterator &operator++() {
    m_current = m_current->next;
    return *this;
  }
 
  using difference_type = ptrdiff_t;
  using value_type = T;  // NOTE: std::remove_cv_t<T> from C++20.
  using pointer = T *;
  using reference = T &;
  using iterator_category = std::forward_iterator_tag;
 
  // EqualityComparable (required for InputIterator).
  bool operator==(const List_STL_Iterator &other) const {
    return m_current == other.m_current;
  }
 
  // InputIterator (required for ForwardIterator).
  bool operator!=(const List_STL_Iterator &other) const {
    return !(*this == other);
  }
 
  T *operator->() const { return static_cast<T *>(m_current->info); }
 
  // DefaultConstructible (required for ForwardIterator).
  List_STL_Iterator() = default;
 
  // ForwardIterator.
  List_STL_Iterator operator++(int) {
    List_STL_Iterator copy = *this;
    m_current = m_current->next;
    return copy;
  }
 
 private:
  list_node *m_current;
};
 
template <typename T>
class base_ilist;
template <typename T>
class base_ilist_iterator;
 
/*
  A simple intrusive list.
 
  NOTE: this inherently unsafe, since we rely on <T> to have
  the same layout as ilink<T> (see base_ilist::sentinel).
  Please consider using a different strategy for linking objects.
*/
 
template <typename T>
class ilink {
  T **prev, *next;
 
 public:
  ilink() : prev(nullptr), next(nullptr) {}
 
  void unlink() {
    /* Extra tests because element doesn't have to be linked */
    if (prev) *prev = next;
    if (next) next->prev = prev;
    prev = nullptr;
    next = nullptr;
  }
 
  friend class base_ilist<T>;
  friend class base_ilist_iterator<T>;
};
 
/* Needed to be able to have an I_List of char* strings in mysqld.cc. */
 
class i_string : public ilink<i_string> {
 public:
  const char *ptr;
  i_string() : ptr(nullptr) {}
  i_string(const char *s) : ptr(s) {}
};
 
/* needed for linked list of two strings for replicate-rewrite-db */
class i_string_pair : public ilink<i_string_pair> {
 public:
  const char *key;
  const char *val;
  i_string_pair() : key(nullptr), val(nullptr) {}
  i_string_pair(const char *key_arg, const char *val_arg)
      : key(key_arg), val(val_arg) {}
};
 
template <class T>
class I_List_iterator;
 
template <typename T>
class base_ilist {
  T *first;
  ilink<T> sentinel;
 
  static_assert(!std::is_polymorphic<T>::value,
                "Do not use this for classes with virtual members");
 
 public:
  // The sentinel is not a T, but at least it is a POD
  void clear() SUPPRESS_UBSAN {
    first = static_cast<T *>(&sentinel);
    sentinel.prev = &first;
  }
  base_ilist() { clear(); }
 
  // The sentinel is not a T, but at least it is a POD
  bool is_empty() const SUPPRESS_UBSAN {
    return first == static_cast<const T *>(&sentinel);
  }
 
  /// Pushes new element in front of list.
  void push_front(T *a) {
    first->prev = &a->next;
    a->next = first;
    a->prev = &first;
    first = a;
  }
 
  /// Pushes new element to the end of the list, i.e. in front of the sentinel.
  void push_back(T *a) {
    *sentinel.prev = a;
    a->next = static_cast<T *>(&sentinel);
    a->prev = sentinel.prev;
    sentinel.prev = &a->next;
  }
 
  // Unlink first element, and return it.
  T *get() {
    if (is_empty()) return nullptr;
    T *first_link = first;
    first_link->unlink();
    return first_link;
  }
 
  T *head() { return is_empty() ? nullptr : first; }
 
  /**
    Moves list elements to new owner, and empties current owner (i.e. this).
 
    @param[in,out]  new_owner  The new owner of the list elements.
                               Should be empty in input.
  */
 
  void move_elements_to(base_ilist *new_owner) {
    assert(new_owner->is_empty());
    new_owner->first = first;
    new_owner->sentinel = sentinel;
    clear();
  }
 
  friend class base_ilist_iterator<T>;
 
 private:
  /*
    We don't want to allow copying of this class, as that would give us
    two list heads containing the same elements.
    So we declare, but don't define copy CTOR and assignment operator.
  */
  base_ilist(const base_ilist &);
  void operator=(const base_ilist &);
};
 
template <typename T>
class base_ilist_iterator {
  base_ilist<T> *list;
  T **el, *current;
 
 public:
  base_ilist_iterator(base_ilist<T> &list_par)
      : list(&list_par), el(&list_par.first), current(nullptr) {}
 
  // The sentinel is not a T, but at least it is a POD
  T *next(void) SUPPRESS_UBSAN {
    /* This is coded to allow push_back() while iterating */
    current = *el;
    if (current == static_cast<T *>(&list->sentinel)) return nullptr;
    el = &current->next;
    return current;
  }
};
 
template <class T>
class I_List : private base_ilist<T> {
 public:
  using base_ilist<T>::clear;
  using base_ilist<T>::is_empty;
  using base_ilist<T>::get;
  using base_ilist<T>::push_front;
  using base_ilist<T>::push_back;
  using base_ilist<T>::head;
  void move_elements_to(I_List<T> *new_owner) {
    base_ilist<T>::move_elements_to(new_owner);
  }
  friend class I_List_iterator<T>;
};
 
template <class T>
class I_List_iterator : public base_ilist_iterator<T> {
 public:
  I_List_iterator(I_List<T> &a) : base_ilist_iterator<T>(a) {}
  inline T *operator++(int) { return base_ilist_iterator<T>::next(); }
};
 
void free_list(I_List<i_string> *list);
 
#endif  // INCLUDES_MYSQL_SQL_LIST_H