runtime/base/stl_util.h

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_RUNTIME_BASE_STL_UTIL_H_
#define ART_RUNTIME_BASE_STL_UTIL_H_

#include <algorithm>
#include <set>
#include <sstream>

#include "base/logging.h"

namespace art {

// Sort and remove duplicates of an STL vector or deque.
template<class T>
void STLSortAndRemoveDuplicates(T* v) {
  std::sort(v->begin(), v->end());
  v->erase(std::unique(v->begin(), v->end()), v->end());
}

// 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;
  }
}

// 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
// using a container of std::unique_ptr, which ensures that your container's
// elements are deleted when the container goes out of scope.
template <class T>
void STLDeleteElements(T *container) {
  if (container != nullptr) {
    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 != nullptr) {
    for (typename T::iterator i = v->begin(); i != v->end(); ++i) {
      delete i->second;
    }
    v->clear();
  }
}

template <class T>
std::string ToString(const T& v) {
  std::ostringstream os;
  os << "[";
  for (size_t i = 0; i < v.size(); ++i) {
    os << v[i];
    if (i < v.size() - 1) {
      os << ", ";
    }
  }
  os << "]";
  return os.str();
}

// Deleter using free() for use with std::unique_ptr<>. See also UniqueCPtr<> below.
struct FreeDelete {
  // NOTE: Deleting a const object is valid but free() takes a non-const pointer.
  void operator()(const void* ptr) const {
    free(const_cast<void*>(ptr));
  }
};

// Alias for std::unique_ptr<> that uses the C function free() to delete objects.
template <typename T>
using UniqueCPtr = std::unique_ptr<T, FreeDelete>;

// C++14 from-the-future import (std::make_unique)
// Invoke the constructor of 'T' with the provided args, and wrap the result in a unique ptr.
template <typename T, typename ... Args>
std::unique_ptr<T> MakeUnique(Args&& ... args) {
  return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
}

// Find index of the first element with the specified value known to be in the container.
template <typename Container, typename T>
size_t IndexOfElement(const Container& container, const T& value) {
  auto it = std::find(container.begin(), container.end(), value);
  DCHECK(it != container.end());  // Must exist.
  return std::distance(container.begin(), it);
}

// Remove the first element with the specified value known to be in the container.
template <typename Container, typename T>
void RemoveElement(Container& container, const T& value) {
  auto it = std::find(container.begin(), container.end(), value);
  DCHECK(it != container.end());  // Must exist.
  container.erase(it);
}

// Replace the first element with the specified old_value known to be in the container.
template <typename Container, typename T>
void ReplaceElement(Container& container, const T& old_value, const T& new_value) {
  auto it = std::find(container.begin(), container.end(), old_value);
  DCHECK(it != container.end());  // Must exist.
  *it = new_value;
}

// Search for an element with the specified value and return true if it was found, false otherwise.
template <typename Container, typename T>
bool ContainsElement(const Container& container, const T& value, size_t start_pos = 0u) {
  DCHECK_LE(start_pos, container.size());
  auto start = container.begin();
  std::advance(start, start_pos);
  auto it = std::find(start, container.end(), value);
  return it != container.end();
}

// const char* compare function suitable for std::map or std::set.
struct CStringLess {
  bool operator()(const char* lhs, const char* rhs) const {
    return strcmp(lhs, rhs) < 0;
  }
};

// 32-bit FNV-1a hash function suitable for std::unordered_map.
// It can be used with any container which works with range-based for loop.
// See http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function
template <typename Vector>
struct FNVHash {
  size_t operator()(const Vector& vector) const {
    uint32_t hash = 2166136261u;
    for (const auto& value : vector) {
      hash = (hash ^ value) * 16777619u;
    }
    return hash;
  }
};

// Use to suppress type deduction for a function argument.
// See std::identity<> for more background:
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1856.html#20.2.2 - move/forward helpers
//
// e.g. "template <typename X> void bar(identity<X>::type foo);
//     bar(5); // compilation error
//     bar<int>(5); // ok
// or "template <typename T> void foo(T* x, typename Identity<T*>::type y);
//     Base b;
//     Derived d;
//     foo(&b, &d);  // Use implicit Derived* -> Base* conversion.
// If T was deduced from both &b and &d, there would be a mismatch, i.e. deduction failure.
template <typename T>
struct Identity {
  using type = T;
};

// Merge `other` entries into `to_update`.
template <typename T>
static inline void MergeSets(std::set<T>& to_update, const std::set<T>& other) {
  to_update.insert(other.begin(), other.end());
}

}  // namespace art

#endif  // ART_RUNTIME_BASE_STL_UTIL_H_