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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#ifndef STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
#define STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
namespace leveldb {
// A internal wrapper class with an interface similar to Iterator that
// caches the valid() and key() results for an underlying iterator.
// This can help avoid virtual function calls and also gives better
// cache locality.
class IteratorWrapper {
public:
IteratorWrapper(): iter_(NULL), valid_(false) { }
explicit IteratorWrapper(Iterator* iter): iter_(NULL) {
Set(iter);
}
~IteratorWrapper() { delete iter_; }
Iterator* iter() const { return iter_; }
// Takes ownership of "iter" and will delete it when destroyed, or
// when Set() is invoked again.
void Set(Iterator* iter) {
delete iter_;
iter_ = iter;
if (iter_ == NULL) {
valid_ = false;
} else {
Update();
}
}
// Iterator interface methods
bool Valid() const { return valid_; }
Slice key() const { assert(Valid()); return key_; }
Slice value() const { assert(Valid()); return iter_->value(); }
// Methods below require iter() != NULL
Status status() const { assert(iter_); return iter_->status(); }
void Next() { assert(iter_); iter_->Next(); Update(); }
void Prev() { assert(iter_); iter_->Prev(); Update(); }
void Seek(const Slice& k) { assert(iter_); iter_->Seek(k); Update(); }
void SeekToFirst() { assert(iter_); iter_->SeekToFirst(); Update(); }
void SeekToLast() { assert(iter_); iter_->SeekToLast(); Update(); }
private:
void Update() {
valid_ = iter_->Valid();
if (valid_) {
key_ = iter_->key();
}
}
Iterator* iter_;
bool valid_;
Slice key_;
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_TABLE_ITERATOR_WRAPPER_H_
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