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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_