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28 
29 // This is a copy of breakpad's standalone scoped_ptr, which has been
30 // renamed to nonstd::unique_ptr, and from which more complicated classes
31 // have been removed. The reset() method has also been tweaked to more
32 // closely match c++11, and an implicit conversion to bool has been added.
33 
34 // Scopers help you manage ownership of a pointer, helping you easily manage the
35 // a pointer within a scope, and automatically destroying the pointer at the
36 // end of a scope.
37 //
38 // A unique_ptr<T> is like a T*, except that the destructor of unique_ptr<T>
39 // automatically deletes the pointer it holds (if any).
40 // That is, unique_ptr<T> owns the T object that it points to.
41 // Like a T*, a unique_ptr<T> may hold either NULL or a pointer to a T object.
42 // Also like T*, unique_ptr<T> is thread-compatible, and once you
43 // dereference it, you get the thread safety guarantees of T.
44 //
45 // Example usage (unique_ptr):
46 //   {
47 //     unique_ptr<Foo> foo(new Foo("wee"));
48 //   }  // foo goes out of scope, releasing the pointer with it.
49 //
50 //   {
51 //     unique_ptr<Foo> foo;          // No pointer managed.
52 //     foo.reset(new Foo("wee"));    // Now a pointer is managed.
53 //     foo.reset(new Foo("wee2"));   // Foo("wee") was destroyed.
54 //     foo.reset(new Foo("wee3"));   // Foo("wee2") was destroyed.
55 //     foo->Method();                // Foo::Method() called.
56 //     foo.get()->Method();          // Foo::Method() called.
57 //     SomeFunc(foo.release());      // SomeFunc takes ownership, foo no longer
58 //                                   // manages a pointer.
59 //     foo.reset(new Foo("wee4"));   // foo manages a pointer again.
60 //     foo.reset();                  // Foo("wee4") destroyed, foo no longer
61 //                                   // manages a pointer.
62 //   }  // foo wasn't managing a pointer, so nothing was destroyed.
63 //
64 // The size of a unique_ptr is small: sizeof(unique_ptr<C>) == sizeof(C*)
65 
66 #ifndef NONSTD_UNIQUE_PTR_H_
67 #define NONSTD_UNIQUE_PTR_H_
68 
69 // This is an implementation designed to match the anticipated future TR2
70 // implementation of the unique_ptr class.
71 
72 #include <assert.h>
73 #include <stddef.h>
74 #include <stdlib.h>
75 
76 namespace nonstd {
77 
78 // Common implementation for both pointers to elements and pointers to
79 // arrays. These are differentiated below based on the need to invoke
80 // delete vs. delete[] as appropriate.
81 template <class C>
82 class unique_ptr_base {
83  public:
84 
85   // The element type
86   typedef C element_type;
87 
unique_ptr_base(C * p)88   explicit unique_ptr_base(C* p) : ptr_(p) { }
89 
90   // Accessors to get the owned object.
91   // operator* and operator-> will assert() if there is no current object.
92   C& operator*() const {
93     assert(ptr_ != NULL);
94     return *ptr_;
95   }
96   C* operator->() const  {
97     assert(ptr_ != NULL);
98     return ptr_;
99   }
get()100   C* get() const { return ptr_; }
101 
102   // Comparison operators.
103   // These return whether two unique_ptr refer to the same object, not just to
104   // two different but equal objects.
105   bool operator==(C* p) const { return ptr_ == p; }
106   bool operator!=(C* p) const { return ptr_ != p; }
107 
108   // Swap two scoped pointers.
swap(unique_ptr_base & p2)109   void swap(unique_ptr_base& p2) {
110     C* tmp = ptr_;
111     ptr_ = p2.ptr_;
112     p2.ptr_ = tmp;
113   }
114 
115   // Release a pointer.
116   // The return value is the current pointer held by this object.
117   // If this object holds a NULL pointer, the return value is NULL.
118   // After this operation, this object will hold a NULL pointer,
119   // and will not own the object any more.
release()120   C* release() {
121     C* retVal = ptr_;
122     ptr_ = NULL;
123     return retVal;
124   }
125 
126   // Allow promotion to bool for conditional statements.
127   operator bool() const { return ptr_ != NULL; }
128 
129  protected:
130   C* ptr_;
131 };
132 
133 // Implementation for ordinary pointers using delete.
134 template <class C>
135 class unique_ptr : public unique_ptr_base<C> {
136  public:
137   using unique_ptr_base<C>::ptr_;
138 
139   // Constructor. Defaults to initializing with NULL. There is no way
140   // to create an uninitialized unique_ptr. The input parameter must be
141   // allocated with new (not new[] - see below).
142   explicit unique_ptr(C* p = NULL) : unique_ptr_base<C>(p) { }
143 
144   // Destructor.  If there is a C object, delete it.
145   // We don't need to test ptr_ == NULL because C++ does that for us.
~unique_ptr()146   ~unique_ptr() {
147     enum { type_must_be_complete = sizeof(C) };
148     delete ptr_;
149   }
150 
151   // Reset.  Deletes the current owned object, if any.
152   // Then takes ownership of a new object, if given.
153   // this->reset(this->get()) works.
154   void reset(C* p = NULL) {
155     if (p != ptr_) {
156       enum { type_must_be_complete = sizeof(C) };
157       C* old_ptr = ptr_;
158       ptr_ = p;
159       delete old_ptr;
160     }
161   }
162 
163 private:
164   // Forbid comparison of unique_ptr types.  If C2 != C, it totally doesn't
165   // make sense, and if C2 == C, it still doesn't make sense because you should
166   // never have the same object owned by two different unique_ptrs.
167   template <class C2> bool operator==(unique_ptr<C2> const& p2) const;
168   template <class C2> bool operator!=(unique_ptr<C2> const& p2) const;
169 
170   // Disallow evil constructors
171   unique_ptr(const unique_ptr&);
172   void operator=(const unique_ptr&);
173 };
174 
175 // Specialization for arrays using delete[].
176 template <class C>
177 class unique_ptr<C[]> : public unique_ptr_base<C> {
178  public:
179   using unique_ptr_base<C>::ptr_;
180 
181   // Constructor. Defaults to initializing with NULL. There is no way
182   // to create an uninitialized unique_ptr. The input parameter must be
183   // allocated with new[] (not new - see above).
184   explicit unique_ptr(C* p = NULL) : unique_ptr_base<C>(p) { }
185 
186   // Destructor.  If there is a C object, delete it.
187   // We don't need to test ptr_ == NULL because C++ does that for us.
~unique_ptr()188   ~unique_ptr() {
189     enum { type_must_be_complete = sizeof(C) };
190     delete[] ptr_;
191   }
192 
193   // Reset.  Deletes the current owned object, if any.
194   // Then takes ownership of a new object, if given.
195   // this->reset(this->get()) works.
196   void reset(C* p = NULL) {
197     if (p != ptr_) {
198       enum { type_must_be_complete = sizeof(C) };
199       C* old_ptr = ptr_;
200       ptr_ = p;
201       delete[] old_ptr;
202     }
203   }
204 
205   // Support indexing since it is holding array.
206   C& operator[] (size_t i) { return ptr_[i]; }
207 
208 private:
209   // Forbid comparison of unique_ptr types.  If C2 != C, it totally doesn't
210   // make sense, and if C2 == C, it still doesn't make sense because you should
211   // never have the same object owned by two different unique_ptrs.
212   template <class C2> bool operator==(unique_ptr<C2> const& p2) const;
213   template <class C2> bool operator!=(unique_ptr<C2> const& p2) const;
214 
215   // Disallow evil constructors
216   unique_ptr(const unique_ptr&);
217   void operator=(const unique_ptr&);
218 };
219 
220 // Free functions
221 template <class C>
swap(unique_ptr<C> & p1,unique_ptr<C> & p2)222 void swap(unique_ptr<C>& p1, unique_ptr<C>& p2) {
223   p1.swap(p2);
224 }
225 
226 template <class C>
227 bool operator==(C* p1, const unique_ptr<C>& p2) {
228   return p1 == p2.get();
229 }
230 
231 template <class C>
232 bool operator!=(C* p1, const unique_ptr<C>& p2) {
233   return p1 != p2.get();
234 }
235 
236 }  // namespace nonstd
237 
238 #endif  // NONSTD_UNIQUE_PTR_H_
239