smart-pointers.h 3.47 KB
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// Copyright 2011 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
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#ifndef V8_SMART_POINTERS_H_
#define V8_SMART_POINTERS_H_
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namespace v8 {
namespace internal {
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template<typename Deallocator, typename T>
class SmartPointerBase {
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 public:
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  // Default constructor. Constructs an empty scoped pointer.
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  SmartPointerBase() : p_(NULL) {}
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  // Constructs a scoped pointer from a plain one.
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  explicit SmartPointerBase(T* ptr) : p_(ptr) {}
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  // Copy constructor removes the pointer from the original to avoid double
  // freeing.
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  SmartPointerBase(const SmartPointerBase<Deallocator, T>& rhs)
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      : p_(rhs.p_) {
    const_cast<SmartPointerBase<Deallocator, T>&>(rhs).p_ = NULL;
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  }

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  T* operator->() const { return p_; }
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  T& operator*() const { return *p_; }
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  T* get() const { return p_; }
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  // You can use [n] to index as if it was a plain pointer.
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  T& operator[](size_t i) {
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    return p_[i];
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  }
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  // You can use [n] to index as if it was a plain pointer.
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  const T& operator[](size_t i) const {
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    return p_[i];
  }

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  // We don't have implicit conversion to a T* since that hinders migration:
  // You would not be able to change a method from returning a T* to
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  // returning an SmartArrayPointer<T> and then get errors wherever it is used.
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  // If you want to take out the plain pointer and don't want it automatically
  // deleted then call Detach().  Afterwards, the smart pointer is empty
  // (NULL).
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  T* Detach() {
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    T* temp = p_;
    p_ = NULL;
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    return temp;
  }

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  void Reset(T* new_value) {
    ASSERT(p_ == NULL || p_ != new_value);
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    if (p_) Deallocator::Delete(p_);
    p_ = new_value;
  }

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  // Assignment requires an empty (NULL) SmartArrayPointer as the receiver. Like
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  // the copy constructor it removes the pointer in the original to avoid
  // double freeing.
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  SmartPointerBase<Deallocator, T>& operator=(
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      const SmartPointerBase<Deallocator, T>& rhs) {
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    ASSERT(is_empty());
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    T* tmp = rhs.p_;  // swap to handle self-assignment
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    const_cast<SmartPointerBase<Deallocator, T>&>(rhs).p_ = NULL;
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    p_ = tmp;
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    return *this;
  }

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  bool is_empty() const { return p_ == NULL; }

 protected:
  // When the destructor of the scoped pointer is executed the plain pointer
  // is deleted using DeleteArray.  This implies that you must allocate with
  // NewArray.
  ~SmartPointerBase() { if (p_) Deallocator::Delete(p_); }
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 private:
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  T* p_;
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};

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// A 'scoped array pointer' that calls DeleteArray on its pointer when the
// destructor is called.

template<typename T>
struct ArrayDeallocator {
  static void Delete(T* array) {
    DeleteArray(array);
  }
};


template<typename T>
class SmartArrayPointer: public SmartPointerBase<ArrayDeallocator<T>, T> {
 public:
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  SmartArrayPointer() { }
  explicit SmartArrayPointer(T* ptr)
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      : SmartPointerBase<ArrayDeallocator<T>, T>(ptr) { }
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  SmartArrayPointer(const SmartArrayPointer<T>& rhs)
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      : SmartPointerBase<ArrayDeallocator<T>, T>(rhs) { }
};


template<typename T>
struct ObjectDeallocator {
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  static void Delete(T* object) {
    delete object;
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  }
};

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template<typename T>
class SmartPointer: public SmartPointerBase<ObjectDeallocator<T>, T> {
 public:
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  SmartPointer() { }
  explicit SmartPointer(T* ptr)
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      : SmartPointerBase<ObjectDeallocator<T>, T>(ptr) { }
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  SmartPointer(const SmartPointer<T>& rhs)
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      : SmartPointerBase<ObjectDeallocator<T>, T>(rhs) { }
};

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} }  // namespace v8::internal

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#endif  // V8_SMART_POINTERS_H_