tesseract  5.0.0-alpha-619-ge9db
doubleptr.h
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1 // Copyright 2012 Google Inc. All Rights Reserved.
2 // Author: rays@google.com (Ray Smith)
4 // File: doubleptr.h
5 // Description: Double-ended pointer that keeps pointing correctly even
6 // when reallocated or copied.
7 // Author: Ray Smith
8 // Created: Wed Mar 14 12:22:57 PDT 2012
9 //
10 // (C) Copyright 2012, Google Inc.
11 // Licensed under the Apache License, Version 2.0 (the "License");
12 // you may not use this file except in compliance with the License.
13 // You may obtain a copy of the License at
14 // http://www.apache.org/licenses/LICENSE-2.0
15 // Unless required by applicable law or agreed to in writing, software
16 // distributed under the License is distributed on an "AS IS" BASIS,
17 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
18 // See the License for the specific language governing permissions and
19 // limitations under the License.
20 //
22 
23 #ifndef TESSERACT_CCUTIL_DOUBLEPTR_H_
24 #define TESSERACT_CCUTIL_DOUBLEPTR_H_
25 
26 #include "errcode.h"
27 
28 namespace tesseract {
29 
30 // A smart pointer class that implements a double-ended pointer. Each end
31 // points to the other end. The copy constructor and operator= have MOVE
32 // semantics, meaning that the relationship with the other end moves to the
33 // destination of the copy, leaving the source unattached.
34 // For this reason both the copy constructor and the operator= take a non-const
35 // reference argument, and the const reference versions cannot be used.
36 // DoublePtr is useful to incorporate into structures that are part of a
37 // collection such as GenericVector or STL containers, where reallocs can
38 // relocate the members. DoublePtr is also useful in a GenericHeap, where it
39 // can correctly maintain the pointer to an element of the heap despite it
40 // getting moved around on the heap.
41 class DoublePtr {
42  public:
43  DoublePtr() : other_end_(nullptr) {}
44  // Copy constructor steals the partner off src and is therefore a non
45  // const reference arg.
46  // Copying a const DoublePtr generates a compiler error.
48  other_end_ = src.other_end_;
49  if (other_end_ != nullptr) {
50  other_end_->other_end_ = this;
51  src.other_end_ = nullptr;
52  }
53  }
54  // Operator= steals the partner off src, and therefore needs src to be a non-
55  // const reference.
56  // Assigning from a const DoublePtr generates a compiler error.
57  void operator=(DoublePtr& src) {
58  Disconnect();
59  other_end_ = src.other_end_;
60  if (other_end_ != nullptr) {
61  other_end_->other_end_ = this;
62  src.other_end_ = nullptr;
63  }
64  }
65 
66  // Connects this and other, discarding any existing connections.
67  void Connect(DoublePtr* other) {
68  other->Disconnect();
69  Disconnect();
70  other->other_end_ = this;
71  other_end_ = other;
72  }
73  // Disconnects this and other, making OtherEnd() return nullptr for both.
74  void Disconnect() {
75  if (other_end_ != nullptr) {
76  other_end_->other_end_ = nullptr;
77  other_end_ = nullptr;
78  }
79  }
80  // Returns the pointer to the other end of the double pointer.
81  DoublePtr* OtherEnd() const {
82  return other_end_;
83  }
84 
85  private:
86  // Pointer to the other end of the link. It is always true that either
87  // other_end_ == nullptr or other_end_->other_end_ == this.
88  DoublePtr* other_end_;
89 };
90 
91 } // namespace tesseract.
92 
93 #endif // THIRD_PARTY_TESSERACT_CCUTIL_DOUBLEPTR_H_
tesseract::DoublePtr::DoublePtr
DoublePtr()
Definition: doubleptr.h:43
tesseract::DoublePtr
Definition: doubleptr.h:41
tesseract::DoublePtr::Disconnect
void Disconnect()
Definition: doubleptr.h:74
tesseract::DoublePtr::DoublePtr
DoublePtr(DoublePtr &src)
Definition: doubleptr.h:47
tesseract::DoublePtr::OtherEnd
DoublePtr * OtherEnd() const
Definition: doubleptr.h:81
tesseract
Definition: baseapi.h:65
tesseract::DoublePtr::Connect
void Connect(DoublePtr *other)
Definition: doubleptr.h:67
tesseract::DoublePtr::operator=
void operator=(DoublePtr &src)
Definition: doubleptr.h:57
errcode.h