1
    2
    3
    4
    5
    6
    7
    8
    9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
  100
  101
  102
  103
  104
  105
  106
  107


base / stl_util.h [blame]

// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Derived from google3/util/gtl/stl_util.h

#ifndef BASE_STL_UTIL_H_
#define BASE_STL_UTIL_H_

#include <algorithm>
#include <iterator>

#include "base/check.h"
#include "base/ranges/algorithm.h"

namespace base {

// Returns a const reference to the underlying container of a container adapter.
// Works for std::priority_queue, std::queue, and std::stack.
template <class A>
const typename A::container_type& GetUnderlyingContainer(const A& adapter) {
  struct ExposedAdapter : A {
    using A::c;
  };
  return adapter.*&ExposedAdapter::c;
}

// Clears internal memory of an STL object.
// STL clear()/reserve(0) does not always free internal memory allocated
// This function uses swap/destructor to ensure the internal memory is freed.
template<class T>
void STLClearObject(T* obj) {
  T tmp;
  tmp.swap(*obj);
  // Sometimes "T tmp" allocates objects with memory (arena implementation?).
  // Hence using additional reserve(0) even if it doesn't always work.
  obj->reserve(0);
}

// Returns a new ResultType containing the difference of two sorted containers.
template <typename ResultType, typename Arg1, typename Arg2>
ResultType STLSetDifference(const Arg1& a1, const Arg2& a2) {
  DCHECK(ranges::is_sorted(a1));
  DCHECK(ranges::is_sorted(a2));
  ResultType difference;
  std::set_difference(a1.begin(), a1.end(),
                      a2.begin(), a2.end(),
                      std::inserter(difference, difference.end()));
  return difference;
}

// Returns a new ResultType containing the union of two sorted containers.
template <typename ResultType, typename Arg1, typename Arg2>
ResultType STLSetUnion(const Arg1& a1, const Arg2& a2) {
  DCHECK(ranges::is_sorted(a1));
  DCHECK(ranges::is_sorted(a2));
  ResultType result;
  std::set_union(a1.begin(), a1.end(),
                 a2.begin(), a2.end(),
                 std::inserter(result, result.end()));
  return result;
}

// Returns a new ResultType containing the intersection of two sorted
// containers.
template <typename ResultType, typename Arg1, typename Arg2>
ResultType STLSetIntersection(const Arg1& a1, const Arg2& a2) {
  DCHECK(ranges::is_sorted(a1));
  DCHECK(ranges::is_sorted(a2));
  ResultType result;
  std::set_intersection(a1.begin(), a1.end(),
                        a2.begin(), a2.end(),
                        std::inserter(result, result.end()));
  return result;
}

// A helper class to be used as the predicate with |EraseIf| to implement
// in-place set intersection. Helps implement the algorithm of going through
// each container an element at a time, erasing elements from the first
// container if they aren't in the second container. Requires each container be
// sorted. Note that the logic below appears inverted since it is returning
// whether an element should be erased.
template <class Collection>
class IsNotIn {
 public:
  explicit IsNotIn(const Collection& collection)
      : it_(collection.begin()), end_(collection.end()) {}

  bool operator()(const typename Collection::value_type& x) {
    while (it_ != end_ && *it_ < x) {
      ++it_;
    }
    if (it_ == end_ || *it_ != x) {
      return true;
    }
    ++it_;
    return false;
  }

 private:
  typename Collection::const_iterator it_;
  const typename Collection::const_iterator end_;
};

}  // namespace base

#endif  // BASE_STL_UTIL_H_