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