base/stl_util-inl.h - chromium/src - Git at Google

 // Copyright (c) 2010 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.

 // STL utility functions.  Usually, these replace built-in, but slow(!),
 // STL functions with more efficient versions.

 #ifndef BASE_STL_UTIL_INL_H_
 #define BASE_STL_UTIL_INL_H_
 #pragma once

 #include <string.h>  // for memcpy
 #include <functional>
 #include <set>
 #include <string>
 #include <vector>
 #include <cassert>

 // Clear 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);
   obj->reserve(0);  // this is because sometimes "T tmp" allocates objects with
                     // memory (arena implementation?).  use reserve()
                     // to clear() even if it doesn't always work
 }

 // Reduce memory usage on behalf of object if it is using more than
 // "bytes" bytes of space.  By default, we clear objects over 1MB.
 template <class T> inline void STLClearIfBig(T* obj, size_t limit = 1<<20) {
   if (obj->capacity() >= limit) {
     STLClearObject(obj);
   } else {
     obj->clear();
   }
 }

 // Reserve space for STL object.
 // STL's reserve() will always copy.
 // This function avoid the copy if we already have capacity
 template<class T> void STLReserveIfNeeded(T* obj, int new_size) {
   if (obj->capacity() < new_size)   // increase capacity
     obj->reserve(new_size);
   else if (obj->size() > new_size)  // reduce size
     obj->resize(new_size);
 }

 // STLDeleteContainerPointers()
 //  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;
   }
 }

 // STLDeleteContainerPairPointers()
 //  For a range within a container of pairs, calls delete
 //  (non-array version) on BOTH items in the pairs.
 // NOTE: Like STLDeleteContainerPointers, it is important that this deletes
 // behind the iterator because if both the key and value are deleted, the
 // container may call the hash function on the iterator when it is advanced,
 // which could result in the hash function trying to dereference a stale
 // pointer.
 template <class ForwardIterator>
 void STLDeleteContainerPairPointers(ForwardIterator begin,
                                     ForwardIterator end) {
   while (begin != end) {
     ForwardIterator temp = begin;
     ++begin;
     delete temp->first;
     delete temp->second;
   }
 }

 // STLDeleteContainerPairFirstPointers()
 //  For a range within a container of pairs, calls delete (non-array version)
 //  on the FIRST item in the pairs.
 // NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.
 template <class ForwardIterator>
 void STLDeleteContainerPairFirstPointers(ForwardIterator begin,
                                          ForwardIterator end) {
   while (begin != end) {
     ForwardIterator temp = begin;
     ++begin;
     delete temp->first;
   }
 }

 // STLDeleteContainerPairSecondPointers()
 //  For a range within a container of pairs, calls delete
 //  (non-array version) on the SECOND item in the pairs.
 template <class ForwardIterator>
 void STLDeleteContainerPairSecondPointers(ForwardIterator begin,
                                           ForwardIterator end) {
   while (begin != end) {
     delete begin->second;
     ++begin;
   }
 }

 template<typename T>
 inline void STLAssignToVector(std::vector<T>* vec,
                               const T* ptr,
                               size_t n) {
   vec->resize(n);
   memcpy(&vec->front(), ptr, n*sizeof(T));
 }

 /***** Hack to allow faster assignment to a vector *****/

 // This routine speeds up an assignment of 32 bytes to a vector from
 // about 250 cycles per assignment to about 140 cycles.
 //
 // Usage:
 //      STLAssignToVectorChar(&vec, ptr, size);
 //      STLAssignToString(&str, ptr, size);

 inline void STLAssignToVectorChar(std::vector<char>* vec,
                                   const char* ptr,
                                   size_t n) {
   STLAssignToVector(vec, ptr, n);
 }

 inline void STLAssignToString(std::string* str, const char* ptr, size_t n) {
   str->resize(n);
   memcpy(&*str->begin(), ptr, n);
 }

 // To treat a possibly-empty vector as an array, use these functions.
 // If you know the array will never be empty, you can use &*v.begin()
 // directly, but that is allowed to dump core if v is empty.  This
 // function is the most efficient code that will work, taking into
 // account how our STL is actually implemented.  THIS IS NON-PORTABLE
 // CODE, so call us instead of repeating the nonportable code
 // everywhere.  If our STL implementation changes, we will need to
 // change this as well.

 template<typename T>
 inline T* vector_as_array(std::vector<T>* v) {
 # ifdef NDEBUG
   return &*v->begin();
 # else
   return v->empty() ? NULL : &*v->begin();
 # endif
 }

 template<typename T>
 inline const T* vector_as_array(const std::vector<T>* v) {
 # ifdef NDEBUG
   return &*v->begin();
 # else
   return v->empty() ? NULL : &*v->begin();
 # endif
 }

 // 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())! See the unittest for why.
   return str->empty() ? NULL : &*str->begin();
 }

 // These are methods that test two hash maps/sets for equality.  These exist
 // because the == operator in the STL can return false when the maps/sets
 // contain identical elements.  This is because it compares the internal hash
 // tables which may be different if the order of insertions and deletions
 // differed.

 template <class HashSet>
 inline bool HashSetEquality(const HashSet& set_a, const HashSet& set_b) {
   if (set_a.size() != set_b.size()) return false;
   for (typename HashSet::const_iterator i = set_a.begin();
        i != set_a.end(); ++i) {
     if (set_b.find(*i) == set_b.end())
       return false;
   }
   return true;
 }

 template <class HashMap>
 inline bool HashMapEquality(const HashMap& map_a, const HashMap& map_b) {
   if (map_a.size() != map_b.size()) return false;
   for (typename HashMap::const_iterator i = map_a.begin();
        i != map_a.end(); ++i) {
     typename HashMap::const_iterator j = map_b.find(i->first);
     if (j == map_b.end()) return false;
     if (i->second != j->second) return false;
   }
   return true;
 }

 // 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.
 //
 // As an alternative to calling STLDeleteElements() directly, consider
 // STLElementDeleter (defined below), which ensures that your container's
 // elements are deleted when the STLElementDeleter goes out of scope.
 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 *v) {
   if (!v) return;
   for (typename T::iterator i = v->begin(); i != v->end(); ++i) {
     delete i->second;
   }
   v->clear();
 }


 // The following classes provide a convenient way to delete all elements or
 // values from STL containers when they goes out of scope.  This greatly
 // simplifies code that creates temporary objects and has multiple return
 // statements.  Example:
 //
 // vector<MyProto *> tmp_proto;
 // STLElementDeleter<vector<MyProto *> > d(&tmp_proto);
 // if (...) return false;
 // ...
 // return success;

 // Given a pointer to an STL container this class will delete all the element
 // pointers when it goes out of scope.

 template<class STLContainer> class STLElementDeleter {
  public:
   STLElementDeleter<STLContainer>(STLContainer *ptr) : container_ptr_(ptr) {}
   ~STLElementDeleter<STLContainer>() { STLDeleteElements(container_ptr_); }
  private:
   STLContainer *container_ptr_;
 };

 // Given a pointer to an STL container this class will delete all the value
 // pointers when it goes out of scope.

 template<class STLContainer> class STLValueDeleter {
  public:
   STLValueDeleter<STLContainer>(STLContainer *ptr) : container_ptr_(ptr) {}
   ~STLValueDeleter<STLContainer>() { STLDeleteValues(container_ptr_); }
  private:
   STLContainer *container_ptr_;
 };


 // Forward declare some callback classes in callback.h for STLBinaryFunction
 template <class R, class T1, class T2>
 class ResultCallback2;

 // STLBinaryFunction is a wrapper for the ResultCallback2 class in callback.h
 // It provides an operator () method instead of a Run method, so it may be
 // passed to STL functions in <algorithm>.
 //
 // The client should create callback with NewPermanentCallback, and should
 // delete callback after it is done using the STLBinaryFunction.

 template <class Result, class Arg1, class Arg2>
 class STLBinaryFunction : public std::binary_function<Arg1, Arg2, Result> {
  public:
   typedef ResultCallback2<Result, Arg1, Arg2> Callback;

   STLBinaryFunction(Callback* callback)
     : callback_(callback) {
     assert(callback_);
   }

   Result operator() (Arg1 arg1, Arg2 arg2) {
     return callback_->Run(arg1, arg2);
   }

  private:
   Callback* callback_;
 };

 // STLBinaryPredicate is a specialized version of STLBinaryFunction, where the
 // return type is bool and both arguments have type Arg.  It can be used
 // wherever STL requires a StrictWeakOrdering, such as in sort() or
 // lower_bound().
 //
 // templated typedefs are not supported, so instead we use inheritance.

 template <class Arg>
 class STLBinaryPredicate : public STLBinaryFunction<bool, Arg, Arg> {
  public:
   typedef typename STLBinaryPredicate<Arg>::Callback Callback;
   STLBinaryPredicate(Callback* callback)
     : STLBinaryFunction<bool, Arg, Arg>(callback) {
   }
 };

 // Functors that compose arbitrary unary and binary functions with a
 // function that "projects" one of the members of a pair.
 // Specifically, if p1 and p2, respectively, are the functions that
 // map a pair to its first and second, respectively, members, the
 // table below summarizes the functions that can be constructed:
 //
 // * UnaryOperate1st<pair>(f) returns the function x -> f(p1(x))
 // * UnaryOperate2nd<pair>(f) returns the function x -> f(p2(x))
 // * BinaryOperate1st<pair>(f) returns the function (x,y) -> f(p1(x),p1(y))
 // * BinaryOperate2nd<pair>(f) returns the function (x,y) -> f(p2(x),p2(y))
 //
 // A typical usage for these functions would be when iterating over
 // the contents of an STL map. For other sample usage, see the unittest.

 template<typename Pair, typename UnaryOp>
 class UnaryOperateOnFirst
     : public std::unary_function<Pair, typename UnaryOp::result_type> {
  public:
   UnaryOperateOnFirst() {
   }

   UnaryOperateOnFirst(const UnaryOp& f) : f_(f) {
   }

   typename UnaryOp::result_type operator()(const Pair& p) const {
     return f_(p.first);
   }

  private:
   UnaryOp f_;
 };

 template<typename Pair, typename UnaryOp>
 UnaryOperateOnFirst<Pair, UnaryOp> UnaryOperate1st(const UnaryOp& f) {
   return UnaryOperateOnFirst<Pair, UnaryOp>(f);
 }

 template<typename Pair, typename UnaryOp>
 class UnaryOperateOnSecond
     : public std::unary_function<Pair, typename UnaryOp::result_type> {
  public:
   UnaryOperateOnSecond() {
   }

   UnaryOperateOnSecond(const UnaryOp& f) : f_(f) {
   }

   typename UnaryOp::result_type operator()(const Pair& p) const {
     return f_(p.second);
   }

  private:
   UnaryOp f_;
 };

 template<typename Pair, typename UnaryOp>
 UnaryOperateOnSecond<Pair, UnaryOp> UnaryOperate2nd(const UnaryOp& f) {
   return UnaryOperateOnSecond<Pair, UnaryOp>(f);
 }

 template<typename Pair, typename BinaryOp>
 class BinaryOperateOnFirst
     : public std::binary_function<Pair, Pair, typename BinaryOp::result_type> {
  public:
   BinaryOperateOnFirst() {
   }

   BinaryOperateOnFirst(const BinaryOp& f) : f_(f) {
   }

   typename BinaryOp::result_type operator()(const Pair& p1,
                                             const Pair& p2) const {
     return f_(p1.first, p2.first);
   }

  private:
   BinaryOp f_;
 };

 template<typename Pair, typename BinaryOp>
 BinaryOperateOnFirst<Pair, BinaryOp> BinaryOperate1st(const BinaryOp& f) {
   return BinaryOperateOnFirst<Pair, BinaryOp>(f);
 }

 template<typename Pair, typename BinaryOp>
 class BinaryOperateOnSecond
     : public std::binary_function<Pair, Pair, typename BinaryOp::result_type> {
  public:
   BinaryOperateOnSecond() {
   }

   BinaryOperateOnSecond(const BinaryOp& f) : f_(f) {
   }

   typename BinaryOp::result_type operator()(const Pair& p1,
                                             const Pair& p2) const {
     return f_(p1.second, p2.second);
   }

  private:
   BinaryOp f_;
 };

 template<typename Pair, typename BinaryOp>
 BinaryOperateOnSecond<Pair, BinaryOp> BinaryOperate2nd(const BinaryOp& f) {
   return BinaryOperateOnSecond<Pair, BinaryOp>(f);
 }

 // Translates a set into a vector.
 template<typename T>
 std::vector<T> SetToVector(const std::set<T>& values) {
   std::vector<T> result;
   result.reserve(values.size());
   result.insert(result.begin(), values.begin(), values.end());
   return result;
 }

 // 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();
 }

 #endif  // BASE_STL_UTIL_INL_H_
	// Copyright (c) 2010 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.

	// STL utility functions. Usually, these replace built-in, but slow(!),
	// STL functions with more efficient versions.

	#ifndef BASE_STL_UTIL_INL_H_
	#define BASE_STL_UTIL_INL_H_
	#pragma once

	#include <string.h> // for memcpy
	#include <functional>
	#include <set>
	#include <string>
	#include <vector>
	#include <cassert>

	// Clear 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);
	obj->reserve(0); // this is because sometimes "T tmp" allocates objects with
	// memory (arena implementation?). use reserve()
	// to clear() even if it doesn't always work
	}

	// Reduce memory usage on behalf of object if it is using more than
	// "bytes" bytes of space. By default, we clear objects over 1MB.
	template <class T> inline void STLClearIfBig(T* obj, size_t limit = 1<<20) {
	if (obj->capacity() >= limit) {
	STLClearObject(obj);
	} else {
	obj->clear();
	}
	}

	// Reserve space for STL object.
	// STL's reserve() will always copy.
	// This function avoid the copy if we already have capacity
	template<class T> void STLReserveIfNeeded(T* obj, int new_size) {
	if (obj->capacity() < new_size) // increase capacity
	obj->reserve(new_size);
	else if (obj->size() > new_size) // reduce size
	obj->resize(new_size);
	}

	// STLDeleteContainerPointers()
	// 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;
	}
	}

	// STLDeleteContainerPairPointers()
	// For a range within a container of pairs, calls delete
	// (non-array version) on BOTH items in the pairs.
	// NOTE: Like STLDeleteContainerPointers, it is important that this deletes
	// behind the iterator because if both the key and value are deleted, the
	// container may call the hash function on the iterator when it is advanced,
	// which could result in the hash function trying to dereference a stale
	// pointer.
	template <class ForwardIterator>
	void STLDeleteContainerPairPointers(ForwardIterator begin,
	ForwardIterator end) {
	while (begin != end) {
	ForwardIterator temp = begin;
	++begin;
	delete temp->first;
	delete temp->second;
	}
	}

	// STLDeleteContainerPairFirstPointers()
	// For a range within a container of pairs, calls delete (non-array version)
	// on the FIRST item in the pairs.
	// NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.
	template <class ForwardIterator>
	void STLDeleteContainerPairFirstPointers(ForwardIterator begin,
	ForwardIterator end) {
	while (begin != end) {
	ForwardIterator temp = begin;
	++begin;
	delete temp->first;
	}
	}

	// STLDeleteContainerPairSecondPointers()
	// For a range within a container of pairs, calls delete
	// (non-array version) on the SECOND item in the pairs.
	template <class ForwardIterator>
	void STLDeleteContainerPairSecondPointers(ForwardIterator begin,
	ForwardIterator end) {
	while (begin != end) {
	delete begin->second;
	++begin;
	}
	}

	template<typename T>
	inline void STLAssignToVector(std::vector<T>* vec,
	const T* ptr,
	size_t n) {
	vec->resize(n);
	memcpy(&vec->front(), ptr, n*sizeof(T));
	}

	/*** Hack to allow faster assignment to a vector ***/

	// This routine speeds up an assignment of 32 bytes to a vector from
	// about 250 cycles per assignment to about 140 cycles.
	//
	// Usage:
	// STLAssignToVectorChar(&vec, ptr, size);
	// STLAssignToString(&str, ptr, size);

	inline void STLAssignToVectorChar(std::vector<char>* vec,
	const char* ptr,
	size_t n) {
	STLAssignToVector(vec, ptr, n);
	}

	inline void STLAssignToString(std::string* str, const char* ptr, size_t n) {
	str->resize(n);
	memcpy(&*str->begin(), ptr, n);
	}

	// To treat a possibly-empty vector as an array, use these functions.
	// If you know the array will never be empty, you can use &*v.begin()
	// directly, but that is allowed to dump core if v is empty. This
	// function is the most efficient code that will work, taking into
	// account how our STL is actually implemented. THIS IS NON-PORTABLE
	// CODE, so call us instead of repeating the nonportable code
	// everywhere. If our STL implementation changes, we will need to
	// change this as well.

	template<typename T>
	inline T* vector_as_array(std::vector<T>* v) {
	# ifdef NDEBUG
	return &*v->begin();
	# else
	return v->empty() ? NULL : &*v->begin();
	# endif
	}

	template<typename T>
	inline const T* vector_as_array(const std::vector<T>* v) {
	# ifdef NDEBUG
	return &*v->begin();
	# else
	return v->empty() ? NULL : &*v->begin();
	# endif
	}

	// 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())! See the unittest for why.
	return str->empty() ? NULL : &*str->begin();
	}

	// These are methods that test two hash maps/sets for equality. These exist
	// because the == operator in the STL can return false when the maps/sets
	// contain identical elements. This is because it compares the internal hash
	// tables which may be different if the order of insertions and deletions
	// differed.

	template <class HashSet>
	inline bool HashSetEquality(const HashSet& set_a, const HashSet& set_b) {
	if (set_a.size() != set_b.size()) return false;
	for (typename HashSet::const_iterator i = set_a.begin();
	i != set_a.end(); ++i) {
	if (set_b.find(*i) == set_b.end())
	return false;
	}
	return true;
	}

	template <class HashMap>
	inline bool HashMapEquality(const HashMap& map_a, const HashMap& map_b) {
	if (map_a.size() != map_b.size()) return false;
	for (typename HashMap::const_iterator i = map_a.begin();
	i != map_a.end(); ++i) {
	typename HashMap::const_iterator j = map_b.find(i->first);
	if (j == map_b.end()) return false;
	if (i->second != j->second) return false;
	}
	return true;
	}

	// 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.
	//
	// As an alternative to calling STLDeleteElements() directly, consider
	// STLElementDeleter (defined below), which ensures that your container's
	// elements are deleted when the STLElementDeleter goes out of scope.
	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 *v) {
	if (!v) return;
	for (typename T::iterator i = v->begin(); i != v->end(); ++i) {
	delete i->second;
	}
	v->clear();
	}


	// The following classes provide a convenient way to delete all elements or
	// values from STL containers when they goes out of scope. This greatly
	// simplifies code that creates temporary objects and has multiple return
	// statements. Example:
	//
	// vector<MyProto *> tmp_proto;
	// STLElementDeleter<vector<MyProto *> > d(&tmp_proto);
	// if (...) return false;
	// ...
	// return success;

	// Given a pointer to an STL container this class will delete all the element
	// pointers when it goes out of scope.

	template<class STLContainer> class STLElementDeleter {
	public:
	STLElementDeleter<STLContainer>(STLContainer *ptr) : container_ptr_(ptr) {}
	~STLElementDeleter<STLContainer>() { STLDeleteElements(container_ptr_); }
	private:
	STLContainer *container_ptr_;
	};

	// Given a pointer to an STL container this class will delete all the value
	// pointers when it goes out of scope.

	template<class STLContainer> class STLValueDeleter {
	public:
	STLValueDeleter<STLContainer>(STLContainer *ptr) : container_ptr_(ptr) {}
	~STLValueDeleter<STLContainer>() { STLDeleteValues(container_ptr_); }
	private:
	STLContainer *container_ptr_;
	};


	// Forward declare some callback classes in callback.h for STLBinaryFunction
	template <class R, class T1, class T2>
	class ResultCallback2;

	// STLBinaryFunction is a wrapper for the ResultCallback2 class in callback.h
	// It provides an operator () method instead of a Run method, so it may be
	// passed to STL functions in <algorithm>.
	//
	// The client should create callback with NewPermanentCallback, and should
	// delete callback after it is done using the STLBinaryFunction.

	template <class Result, class Arg1, class Arg2>
	class STLBinaryFunction : public std::binary_function<Arg1, Arg2, Result> {
	public:
	typedef ResultCallback2<Result, Arg1, Arg2> Callback;

	STLBinaryFunction(Callback* callback)
	: callback_(callback) {
	assert(callback_);
	}

	Result operator() (Arg1 arg1, Arg2 arg2) {
	return callback_->Run(arg1, arg2);
	}

	private:
	Callback* callback_;
	};

	// STLBinaryPredicate is a specialized version of STLBinaryFunction, where the
	// return type is bool and both arguments have type Arg. It can be used
	// wherever STL requires a StrictWeakOrdering, such as in sort() or
	// lower_bound().
	//
	// templated typedefs are not supported, so instead we use inheritance.

	template <class Arg>
	class STLBinaryPredicate : public STLBinaryFunction<bool, Arg, Arg> {
	public:
	typedef typename STLBinaryPredicate<Arg>::Callback Callback;
	STLBinaryPredicate(Callback* callback)
	: STLBinaryFunction<bool, Arg, Arg>(callback) {
	}
	};

	// Functors that compose arbitrary unary and binary functions with a
	// function that "projects" one of the members of a pair.
	// Specifically, if p1 and p2, respectively, are the functions that
	// map a pair to its first and second, respectively, members, the
	// table below summarizes the functions that can be constructed:
	//
	// * UnaryOperate1st<pair>(f) returns the function x -> f(p1(x))
	// * UnaryOperate2nd<pair>(f) returns the function x -> f(p2(x))
	// * BinaryOperate1st<pair>(f) returns the function (x,y) -> f(p1(x),p1(y))
	// * BinaryOperate2nd<pair>(f) returns the function (x,y) -> f(p2(x),p2(y))
	//
	// A typical usage for these functions would be when iterating over
	// the contents of an STL map. For other sample usage, see the unittest.

	template<typename Pair, typename UnaryOp>
	class UnaryOperateOnFirst
	: public std::unary_function<Pair, typename UnaryOp::result_type> {
	public:
	UnaryOperateOnFirst() {
	}

	UnaryOperateOnFirst(const UnaryOp& f) : f_(f) {
	}

	typename UnaryOp::result_type operator()(const Pair& p) const {
	return f_(p.first);
	}

	private:
	UnaryOp f_;
	};

	template<typename Pair, typename UnaryOp>
	UnaryOperateOnFirst<Pair, UnaryOp> UnaryOperate1st(const UnaryOp& f) {
	return UnaryOperateOnFirst<Pair, UnaryOp>(f);
	}

	template<typename Pair, typename UnaryOp>
	class UnaryOperateOnSecond
	: public std::unary_function<Pair, typename UnaryOp::result_type> {
	public:
	UnaryOperateOnSecond() {
	}

	UnaryOperateOnSecond(const UnaryOp& f) : f_(f) {
	}

	typename UnaryOp::result_type operator()(const Pair& p) const {
	return f_(p.second);
	}

	private:
	UnaryOp f_;
	};

	template<typename Pair, typename UnaryOp>
	UnaryOperateOnSecond<Pair, UnaryOp> UnaryOperate2nd(const UnaryOp& f) {
	return UnaryOperateOnSecond<Pair, UnaryOp>(f);
	}

	template<typename Pair, typename BinaryOp>
	class BinaryOperateOnFirst
	: public std::binary_function<Pair, Pair, typename BinaryOp::result_type> {
	public:
	BinaryOperateOnFirst() {
	}

	BinaryOperateOnFirst(const BinaryOp& f) : f_(f) {
	}

	typename BinaryOp::result_type operator()(const Pair& p1,
	const Pair& p2) const {
	return f_(p1.first, p2.first);
	}

	private:
	BinaryOp f_;
	};

	template<typename Pair, typename BinaryOp>
	BinaryOperateOnFirst<Pair, BinaryOp> BinaryOperate1st(const BinaryOp& f) {
	return BinaryOperateOnFirst<Pair, BinaryOp>(f);
	}

	template<typename Pair, typename BinaryOp>
	class BinaryOperateOnSecond
	: public std::binary_function<Pair, Pair, typename BinaryOp::result_type> {
	public:
	BinaryOperateOnSecond() {
	}

	BinaryOperateOnSecond(const BinaryOp& f) : f_(f) {
	}

	typename BinaryOp::result_type operator()(const Pair& p1,
	const Pair& p2) const {
	return f_(p1.second, p2.second);
	}

	private:
	BinaryOp f_;
	};

	template<typename Pair, typename BinaryOp>
	BinaryOperateOnSecond<Pair, BinaryOp> BinaryOperate2nd(const BinaryOp& f) {
	return BinaryOperateOnSecond<Pair, BinaryOp>(f);
	}

	// Translates a set into a vector.
	template<typename T>
	std::vector<T> SetToVector(const std::set<T>& values) {
	std::vector<T> result;
	result.reserve(values.size());
	result.insert(result.begin(), values.begin(), values.end());
	return result;
	}

	// 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();
	}

	#endif // BASE_STL_UTIL_INL_H_