base/stl_util.h

// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// 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 <functional>
#include <iterator>
#include <string>
#include <vector>

#include "base/logging.h"

namespace base {

// 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);
}

// For a range within a container of pointers, calls delete (non-array version)
// on these pointers.
// NOTE: for these three functions, we could just implement a DeleteObject
// functor and then call for_each() on the range and functor, but this
// requires us to pull in all of algorithm.h, which seems expensive.
// For hash_[multi]set, it is important that this deletes behind the iterator
// because the hash_set may call the hash function on the iterator when it is
// advanced, which could result in the hash function trying to deference a
// stale pointer.
template <class ForwardIterator>
void STLDeleteContainerPointers(ForwardIterator begin, ForwardIterator end) {
  while (begin != end) {
    ForwardIterator temp = begin;
    ++begin;
    delete *temp;
  }
}

// Counts the number of instances of val in a container.
template <typename Container, typename T>
typename std::iterator_traits<
    typename Container::const_iterator>::difference_type
STLCount(const Container& container, const T& val) {
  return std::count(container.begin(), container.end(), val);
}

// Return a mutable char* pointing to a string's internal buffer,
// which may not be null-terminated. Writing through this pointer will
// modify the string.
//
// string_as_array(&str)[i] is valid for 0 <= i < str.size() until the
// next call to a string method that invalidates iterators.
//
// As of 2006-04, there is no standard-blessed way of getting a
// mutable reference to a string's internal buffer. However, issue 530
// (http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#530)
// proposes this as the method. According to Matt Austern, this should
// already work on all current implementations.
inline char* string_as_array(std::string* str) {
  // DO NOT USE const_cast<char*>(str->data())
  return str->empty() ? NULL : &*str->begin();
}

// The following functions are useful for cleaning up STL containers whose
// elements point to allocated memory.

// STLDeleteElements() deletes all the elements in an STL container and clears
// the container.  This function is suitable for use with a vector, set,
// hash_set, or any other STL container which defines sensible begin(), end(),
// and clear() methods.
//
// If container is NULL, this function is a no-op.
template <class T>
void STLDeleteElements(T* container) {
  if (!container)
    return;
  STLDeleteContainerPointers(container->begin(), container->end());
  container->clear();
}

// Given an STL container consisting of (key, value) pairs, STLDeleteValues
// deletes all the "value" components and clears the container.  Does nothing
// in the case it's given a NULL pointer.
template <class T>
void STLDeleteValues(T* container) {
  if (!container)
    return;

  auto it = container->begin();
  while (it != container->end()) {
    auto temp = it;
    ++it;
    delete temp->second;
  }

  container->clear();
}

// Test to see if a set, map, hash_set or hash_map contains a particular key.
// Returns true if the key is in the collection.
template <typename Collection, typename Key>
bool ContainsKey(const Collection& collection, const Key& key) {
  return collection.find(key) != collection.end();
}

// Test to see if a collection like a vector contains a particular value.
// Returns true if the value is in the collection.
template <typename Collection, typename Value>
bool ContainsValue(const Collection& collection, const Value& value) {
  return std::find(collection.begin(), collection.end(), value) !=
      collection.end();
}

// Returns true if the container is sorted.
template <typename Container>
bool STLIsSorted(const Container& cont) {
  // Note: Use reverse iterator on container to ensure we only require
  // value_type to implement operator<.
  return std::adjacent_find(cont.rbegin(), cont.rend(),
                            std::less<typename Container::value_type>())
      == cont.rend();
}

// 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(STLIsSorted(a1));
  DCHECK(STLIsSorted(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(STLIsSorted(a1));
  DCHECK(STLIsSorted(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(STLIsSorted(a1));
  DCHECK(STLIsSorted(a2));
  ResultType result;
  std::set_intersection(a1.begin(), a1.end(),
                        a2.begin(), a2.end(),
                        std::inserter(result, result.end()));
  return result;
}

// Returns true if the sorted container |a1| contains all elements of the sorted
// container |a2|.
template <typename Arg1, typename Arg2>
bool STLIncludes(const Arg1& a1, const Arg2& a2) {
  DCHECK(STLIsSorted(a1));
  DCHECK(STLIsSorted(a2));
  return std::includes(a1.begin(), a1.end(),
                       a2.begin(), a2.end());
}

}  // namespace base

#endif  // BASE_STL_UTIL_H_