/src/mysql-server/include/template_utils.h

Source
/* Copyright (c) 2013, 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 */

#ifndef TEMPLATE_UTILS_INCLUDED
#define TEMPLATE_UTILS_INCLUDED

#include <algorithm>
#include <cassert>
#include <cctype>
#include <cstddef>
#include <iterator>
#include <type_traits>

/**
  @file include/template_utils.h
*/

/**
  Clears a container, but deletes all objects that the elements point to first.
  @tparam Container_type Container of pointers.
 */
template <typename Container_type>
void delete_container_pointers(Container_type &container) {
  typename Container_type::iterator it1 = container.begin();
  typename Container_type::iterator it2 = container.end();
  for (; it1 != it2; ++it1) {
    delete (*it1);
  }
  container.clear();
}

/**
  Clears a container, but frees all objects that the elements point to first.
  @tparam Container_type Container of pointers.
 */
template <typename Container_type>
void my_free_container_pointers(Container_type &container) {
  typename Container_type::iterator it1 = container.begin();
  typename Container_type::iterator it2 = container.end();
  for (; it1 != it2; ++it1) {
    my_free(*it1);
  }
  container.clear();
}

/**
  Casts from one pointer type, to another, without using
  reinterpret_cast or C-style cast:
    foo *f; bar *b= pointer_cast<bar*>(f);
  This avoids having to do:
    foo *f; bar *b= static_cast<bar*>(static_cast<void*>(f));
 */
template <typename T>
constexpr T pointer_cast(void *p) {
  return static_cast<T>(p);
}

template <typename T>
constexpr T pointer_cast(const void *p) {
  return static_cast<T>(p);
}

/**
  Casts from one pointer type to another in a type hierarchy.
  In debug mode, we verify the cast is indeed legal.

  @tparam Target The descendent type, must be a pointer type.
  @tparam Source The parent type.

  @param arg The pointer to be down-cast.

  @return A pointer of type Target.
*/
template <typename Target, typename Source>
inline Target down_cast(Source *arg) {
  static_assert(
      !std::is_base_of<typename std::remove_pointer<Target>::type,
                       Source>::value,
      "Do not use down_cast for upcasts; use implicit_cast or nothing");
  assert(nullptr != dynamic_cast<Target>(arg));
  return static_cast<Target>(arg);
}

/**
  Casts from one reference type to another in a type hierarchy.
  In debug mode, we verify the cast is indeed legal.

  @tparam Target The descendent type, must be a reference type.
  @tparam Source The parent type.

  @param arg The reference to be down-cast.

  @return A reference of type Target.
*/
template <typename Target, typename Source>
inline Target down_cast(Source &arg) {
  // We still use the pointer version of dynamic_cast, as the
  // reference-accepting version throws exceptions, and we don't want to deal
  // with that.
  static_assert(
      !std::is_base_of<typename std::remove_reference<Target>::type,
                       Source>::value,
      "Do not use down_cast for upcasts; use implicit_cast or nothing");
  assert(dynamic_cast<typename std::remove_reference<Target>::type *>(&arg) !=
         nullptr);
  return static_cast<Target>(arg);
}

/**
   Sometimes the compiler insists that types be the same and does not do any
   implicit conversion. For example:
   Derived1 *a;
   Derived2 *b; // Derived1 and 2 are children classes of Base
   Base *x= cond ? a : b; // Error, need to force a cast.

   Use:
   Base *x= cond ? implicit_cast<Base*>(a) : implicit_cast<Base*>(b);
   static_cast would work too, but would be less safe (allows any
   pointer-to-pointer conversion, not only up-casts).
*/
template <typename To>
inline To implicit_cast(To x) {
  return x;
}

/**
   Utility to allow returning values from functions which can fail
 */
template <class VALUE_TYPE>
struct ReturnValueOrError {
  /** Value returned from function in the normal case. */
  VALUE_TYPE value;

  /** True if an error occurred. */
  bool error;
};

/**
   Number of elements in a constant C array.
 */
template <class T, size_t N>
constexpr size_t array_elements(T (&)[N]) noexcept {
  return N;
}

namespace myu {
/**
  Split a range into sub ranges delimited by elements satisfying a predicate.
  Examines the elements from first to last, exclusive. Each time an element
  which satisfies the splitting predicate is encountered, the action argument's
  operator() is invoked with the starting and past-the-end iterators for the
  current sub-range, even if this is empty. When iteration is complete, action()
  is called on the range between the start of the last subrange and last.

  It must be possible to pass a single element with type const
  InputIt::value_type to is_split_element. It must be possible to pass two
  InputIt arguments to action.

  @param first    Beginning of the range to split.
  @param last     End of the range to split.
  @param pred     Callable which will be invoked on each element in
                  turn to determine if it is a splitting element.
  @param action   Callable which will be invoked with the beginning
                  and one-past-the-end iterators for each subrange.
 */
template <class InputIt, class Pred, class Action>
inline void Split(InputIt first, InputIt last, Pred &&pred, Action &&action) {
  while (first != last) {
    InputIt split = std::find_if(first, last, std::forward<Pred>(pred));
    action(first, split);  // Called even for empty subranges, action must
                           // discard if not wanted
    if (split == last) return;
    first = split + 1;
  }
}

/**
  Search backwards for the first occurrence of an element which does not satisfy
  the trimming predicate, and return an InputIt to the element after it.

  @param first Beginning of the range to search.
  @param last  End of the range to search.
  @param pred  Callable which can be applied to a dereferenced InputIt and which
               returns true if the element should be trimmed.

  @returns InputIt referencing the first element of sub range satisfying the
           trimming predicate at the end of the range. last if no elements
           satisfy the trimming predicate.
 */
template <class InputIt, class Pred>
inline InputIt FindTrimmedEnd(InputIt first, InputIt last, Pred &&pred) {
  return std::find_if_not(std::make_reverse_iterator(last),
                          std::make_reverse_iterator(first),
                          std::forward<Pred>(pred))
      .base();
}

/**
  Searches for a sub range such that no elements before or after fail to
  satisfy the trimming predicate.

  @param first Beginning of the range to search.
  @param last  End of the range to search.
  @param pred  Callable which can be applied to a dereferenced InputIt and which
               returns true if the element should be trimmed.

  @returns Pair of iterators denoting the sub range which does not include the
           leading and trailing sub ranges matching the trimming predicate.
           {last, last} if all elements match the trimming predicate.
 */
template <class InputIt, class Pred>
inline std::pair<InputIt, InputIt> FindTrimmedRange(InputIt first, InputIt last,
                                                    Pred &&pred) {
  InputIt f = std::find_if_not(first, last, std::forward<Pred>(pred));
  return {f, FindTrimmedEnd(f, last, std::forward<Pred>(pred))};
}

/** Convenience lambdas for common predicates. */
const auto IsSpace = [](char c) { return isspace(c); };
const auto IsComma = [](char c) { return c == ','; };

}  // namespace myu
#endif  // TEMPLATE_UTILS_INCLUDED

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Created: 2026-02-14 06:50