1 // Copyright 2016 PDFium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef CORE_FXCRT_MAYBE_OWNED_H_
6 #define CORE_FXCRT_MAYBE_OWNED_H_
7 
8 #include <algorithm>
9 #include <memory>
10 #include <utility>
11 
12 #include "core/fxcrt/fx_memory.h"
13 #include "core/fxcrt/fx_system.h"
14 
15 namespace fxcrt {
16 
17 // A template that can hold either owned or unowned references, and cleans up
18 // appropriately.  Possibly the most pernicious anti-pattern imaginable, but
19 // it crops up throughout the codebase due to a desire to avoid copying-in
20 // objects or data.
21 template <typename T, typename D = std::default_delete<T>>
22 class MaybeOwned {
23  public:
MaybeOwned()24   MaybeOwned() : m_pObj(nullptr) {}
MaybeOwned(T * ptr)25   explicit MaybeOwned(T* ptr) : m_pObj(ptr) {}
MaybeOwned(std::unique_ptr<T,D> ptr)26   explicit MaybeOwned(std::unique_ptr<T, D> ptr)
27       : m_pOwnedObj(std::move(ptr)), m_pObj(m_pOwnedObj.get()) {}
28 
29   MaybeOwned(const MaybeOwned& that) = delete;
MaybeOwned(MaybeOwned && that)30   MaybeOwned(MaybeOwned&& that) noexcept
31       : m_pOwnedObj(that.m_pOwnedObj.release()), m_pObj(that.m_pObj) {
32     that.m_pObj = nullptr;
33   }
34 
Reset(std::unique_ptr<T,D> ptr)35   void Reset(std::unique_ptr<T, D> ptr) {
36     m_pOwnedObj = std::move(ptr);
37     m_pObj = m_pOwnedObj.get();
38   }
39   void Reset(T* ptr = nullptr) {
40     m_pOwnedObj.reset();
41     m_pObj = ptr;
42   }
43 
IsOwned()44   bool IsOwned() const { return !!m_pOwnedObj; }
Get()45   T* Get() const { return m_pObj; }
Release()46   std::unique_ptr<T, D> Release() {
47     ASSERT(IsOwned());
48     return std::move(m_pOwnedObj);
49   }
50 
51   MaybeOwned& operator=(const MaybeOwned& that) = delete;
52   MaybeOwned& operator=(MaybeOwned&& that) {
53     m_pOwnedObj = std::move(that.m_pOwnedObj);
54     m_pObj = that.m_pObj;
55     that.m_pObj = nullptr;
56     return *this;
57   }
58   MaybeOwned& operator=(T* ptr) {
59     Reset(ptr);
60     return *this;
61   }
62   MaybeOwned& operator=(std::unique_ptr<T, D> ptr) {
63     Reset(std::move(ptr));
64     return *this;
65   }
66 
67   bool operator==(const MaybeOwned& that) const { return Get() == that.Get(); }
68   bool operator==(const std::unique_ptr<T, D>& ptr) const {
69     return Get() == ptr.get();
70   }
71   bool operator==(T* ptr) const { return Get() == ptr; }
72 
73   bool operator!=(const MaybeOwned& that) const { return !(*this == that); }
74   bool operator!=(const std::unique_ptr<T, D> ptr) const {
75     return !(*this == ptr);
76   }
77   bool operator!=(T* ptr) const { return !(*this == ptr); }
78 
79   explicit operator bool() const { return !!m_pObj; }
80   T& operator*() const { return *m_pObj; }
81   T* operator->() const { return m_pObj; }
82 
83  private:
84   std::unique_ptr<T, D> m_pOwnedObj;
85   T* m_pObj;
86 };
87 
88 }  // namespace fxcrt
89 
90 using fxcrt::MaybeOwned;
91 
92 #endif  // CORE_FXCRT_MAYBE_OWNED_H_
93