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93 lines
3.4 KiB
C++
93 lines
3.4 KiB
C++
// Copyright 2012 Google Inc. All Rights Reserved.
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// Author: rays@google.com (Ray Smith)
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///////////////////////////////////////////////////////////////////////
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// File: doubleptr.h
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// Description: Double-ended pointer that keeps pointing correctly even
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// when reallocated or copied.
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// Author: Ray Smith
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//
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// (C) Copyright 2012, Google Inc.
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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// http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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///////////////////////////////////////////////////////////////////////
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#ifndef TESSERACT_CCUTIL_DOUBLEPTR_H_
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#define TESSERACT_CCUTIL_DOUBLEPTR_H_
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#include "errcode.h"
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namespace tesseract {
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// A smart pointer class that implements a double-ended pointer. Each end
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// points to the other end. The copy constructor and operator= have MOVE
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// semantics, meaning that the relationship with the other end moves to the
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// destination of the copy, leaving the source unattached.
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// For this reason both the copy constructor and the operator= take a non-const
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// reference argument, and the const reference versions cannot be used.
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// DoublePtr is useful to incorporate into structures that are part of a
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// collection such as STL containers, where reallocs can
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// relocate the members. DoublePtr is also useful in a GenericHeap, where it
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// can correctly maintain the pointer to an element of the heap despite it
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// getting moved around on the heap.
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class DoublePtr {
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public:
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DoublePtr() : other_end_(nullptr) {}
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// Copy constructor steals the partner off src and is therefore a non
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// const reference arg.
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// Copying a const DoublePtr generates a compiler error.
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DoublePtr(const DoublePtr &src) {
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other_end_ = src.other_end_;
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if (other_end_ != nullptr) {
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other_end_->other_end_ = this;
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((DoublePtr &)src).other_end_ = nullptr;
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}
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}
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// Operator= steals the partner off src, and therefore needs src to be a non-
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// const reference.
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// Assigning from a const DoublePtr generates a compiler error.
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void operator=(const DoublePtr &src) {
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Disconnect();
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other_end_ = src.other_end_;
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if (other_end_ != nullptr) {
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other_end_->other_end_ = this;
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((DoublePtr &)src).other_end_ = nullptr;
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}
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}
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// Connects this and other, discarding any existing connections.
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void Connect(DoublePtr *other) {
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other->Disconnect();
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Disconnect();
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other->other_end_ = this;
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other_end_ = other;
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}
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// Disconnects this and other, making OtherEnd() return nullptr for both.
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void Disconnect() {
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if (other_end_ != nullptr) {
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other_end_->other_end_ = nullptr;
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other_end_ = nullptr;
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}
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}
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// Returns the pointer to the other end of the double pointer.
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DoublePtr *OtherEnd() const {
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return other_end_;
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}
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private:
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// Pointer to the other end of the link. It is always true that either
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// other_end_ == nullptr or other_end_->other_end_ == this.
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DoublePtr *other_end_;
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};
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} // namespace tesseract.
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#endif // THIRD_PARTY_TESSERACT_CCUTIL_DOUBLEPTR_H_
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