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/** @file postlist.h
* @brief Abstract base class for postlists.
*/
/* Copyright (C) 2007,2008,2009,2011,2015,2017 Olly Betts
* Copyright (C) 2009 Lemur Consulting Ltd
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef XAPIAN_INCLUDED_POSTLIST_H
#define XAPIAN_INCLUDED_POSTLIST_H
#include <string>
#include "xapian/intrusive_ptr.h"
#include <xapian/types.h>
#include <xapian/postingiterator.h>
#include "backends/positionlist.h"
#include "weight/weightinternal.h"
class OrPositionList;
/// Abstract base class for postlists.
class Xapian::PostingIterator::Internal : public Xapian::Internal::intrusive_base {
/// Don't allow assignment.
void operator=(const Internal &);
/// Don't allow copying.
Internal(const Internal &);
protected:
/// Only constructable as a base class for derived classes.
Internal() { }
public:
/** We have virtual methods and want to be able to delete derived classes
* using a pointer to the base class, so we need a virtual destructor.
*/
virtual ~Internal();
/// Get a lower bound on the number of documents indexed by this term.
virtual Xapian::doccount get_termfreq_min() const = 0;
/// Get an upper bound on the number of documents indexed by this term.
virtual Xapian::doccount get_termfreq_max() const = 0;
/** Get an estimate of the number of documents indexed by this term.
*
* It should always be true that:
* get_termfreq_min() <= get_termfreq_est() <= get_termfreq_max()
*/
virtual Xapian::doccount get_termfreq_est() const = 0;
/** Get an estimate for the termfreq and reltermfreq, given the stats.
*
* The frequencies may be for a combination of databases, or for just the
* relevant documents, so the results need not lie in the bounds given by
* get_termfreq_min() and get_termfreq_max().
*/
virtual TermFreqs get_termfreq_est_using_stats(
const Xapian::Weight::Internal & stats) const;
/// Return an upper bound on what get_weight() can return.
virtual double get_maxweight() const = 0;
/// Return the current docid.
virtual Xapian::docid get_docid() const = 0;
/// Return the length of current document.
virtual Xapian::termcount get_doclength() const = 0;
/* FIXME: Once flint has been retired, we should probably strip out
* PostList::get_doclength() and just fetch it from the DB directly.
*/
/// Return the number of unique terms in the current document.
virtual Xapian::termcount get_unique_terms() const = 0;
/** Return the wdf for the document at the current position.
*
* The default implementation throws Xapian::UnimplementedError.
*/
virtual Xapian::termcount get_wdf() const;
/// Return the weight contribution for the current position.
virtual double get_weight() const = 0;
virtual const std::string * get_sort_key() const;
/** If the collapse key is already known, return it.
*
* This is implemented by MSetPostList (and MergePostList). Other
* subclasses rely on the default implementation which just returns
* NULL.
*/
virtual const std::string * get_collapse_key() const;
/// Return true if the current position is past the last entry in this list.
virtual bool at_end() const = 0;
/** Recalculate the upper bound on what get_weight() can return.
*
* If the tree has pruned, get_maxweight() may use cached values. Calling
* this method instead forces a full recalculation.
*
* Note that this method may be called after the postlist has reached the
* end. In this situation, the method should return 0.
*/
virtual double recalc_maxweight() = 0;
/** Read the position list for the term in the current document and
* return a pointer to it (owned by the PostList).
*
* The default implementation throws Xapian::UnimplementedError.
*/
virtual PositionList * read_position_list();
/** Read the position list for the term in the current document and
* return a pointer to it (not owned by the PostList).
*
* The default implementation throws Xapian::UnimplementedError.
*/
virtual PositionList * open_position_list() const;
/** Advance the current position to the next document in the postlist.
*
* The list starts before the first entry in the list, so next()
* must be called before any methods which need the context of
* the current position.
*
* @param w_min The minimum weight contribution that is needed (this is
* just a hint which PostList subclasses may ignore).
*
* @return If a non-NULL pointer is returned, then the caller should
* substitute the returned pointer for its pointer to us, and then
* delete us. This "pruning" can only happen for a non-leaf
* subclass of this class.
*/
virtual Internal * next(double w_min) = 0;
/** Skip forward to the specified docid.
*
* If the specified docid isn't in the list, position ourselves on the
* first document after it (or at_end() if no greater docids are present).
*
* @param w_min The minimum weight contribution that is needed (this is
* just a hint which PostList subclasses may ignore).
*
* @return If a non-NULL pointer is returned, then the caller should
* substitute the returned pointer for its pointer to us, and then
* delete us. This "pruning" can only happen for a non-leaf
* subclass of this class.
*/
virtual Internal * skip_to(Xapian::docid, double w_min) = 0;
/** Check if the specified docid occurs in this postlist.
*
* The caller is required to ensure that the specified @a docid actually
* exists in the database.
*
* This method acts like skip_to() if that can be done at little extra
* cost, in which case it then sets @a valid to true.
*
* Otherwise it simply checks if a particular docid is present. If it
* is, @a valid is set to true. If it isn't, it sets @a valid to
* false, and leaves the position unspecified (and hence the result of
* calling methods which depends on the current position, such as
* get_docid(), are also unspecified). In this state, next() will
* advance to the first matching position after @a docid, and skip_to()
* will act as it would if the position was the first matching position
* after @a docid.
*
* The default implementation calls skip_to().
*/
virtual Internal * check(Xapian::docid did, double w_min, bool &valid);
/** Advance the current position to the next document in the postlist.
*
* Any weight contribution is acceptable.
*/
Internal * next() { return next(0.0); }
/** Skip forward to the specified docid.
*
* Any weight contribution is acceptable.
*/
Internal * skip_to(Xapian::docid did) { return skip_to(did, 0.0); }
/// Count the number of leaf subqueries which match at the current position.
virtual Xapian::termcount count_matching_subqs() const;
/// Gather PositionList* objects for a subtree.
virtual void gather_position_lists(OrPositionList* orposlist);
/// Return a string description of this object.
virtual std::string get_description() const = 0;
};
// In the external API headers, this class is Xapian::PostingIterator::Internal,
// but in the library code it's still known as "PostList" in most places.
typedef Xapian::PostingIterator::Internal PostList;
#endif // XAPIAN_INCLUDED_POSTLIST_H
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