xapian-core/include/xapian/valueiterator.h

   1 /** @file
   2  *  @brief Class for iterating over document values.
   3  */
   4 /* Copyright (C) 2008,2009,2010,2011,2012,2013,2014,2015 Olly Betts
   5  *
   6  * This program is free software; you can redistribute it and/or
   7  * modify it under the terms of the GNU General Public License as
   8  * published by the Free Software Foundation; either version 2 of the
   9  * License, or (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
  19  * USA
  20  */
  21
  22 #ifndef XAPIAN_INCLUDED_VALUEITERATOR_H
  23 #define XAPIAN_INCLUDED_VALUEITERATOR_H
  24
  25 #if !defined XAPIAN_IN_XAPIAN_H && !defined XAPIAN_LIB_BUILD
  26 # error Never use <xapian/valueiterator.h> directly; include <xapian.h> instead.
  27 #endif
  28
  29 #include <iterator>
  30 #include <string>
  31
  32 #include <xapian/attributes.h>
  33 #include <xapian/derefwrapper.h>
  34 #include <xapian/types.h>
  35 #include <xapian/visibility.h>
  36
  37 namespace Xapian {
  38
  39 /// Class for iterating over document values.
  40 class XAPIAN_VISIBILITY_DEFAULT ValueIterator {
  41     void decref();
  42
  43   public:
  44     /// Class representing the ValueIterator internals.
  45     class Internal;
  46     /// @private @internal Reference counted internals.
  47     Internal * internal;
  48
  49     /** @private @internal Wrap an existing Internal. */
  50     XAPIAN_VISIBILITY_INTERNAL
  51     explicit ValueIterator(Internal *internal_);
  52
  53     /// Copy constructor.
  54     ValueIterator(const ValueIterator & o);
  55
  56     /// Assignment.
  57     ValueIterator & operator=(const ValueIterator & o);
  58
  59     /// Move constructor.
  60     ValueIterator(ValueIterator && o)
  61         : internal(o.internal) {
  62         o.internal = nullptr;
  63     }
  64
  65     /// Move assignment operator.
  66     ValueIterator & operator=(ValueIterator && o) {
  67         if (this != &o) {
  68             if (internal) decref();
  69             internal = o.internal;
  70             o.internal = nullptr;
  71         }
  72         return *this;
  73     }
  74
  75     /** Default constructor.
  76      *
  77      *  Creates an uninitialised iterator, which can't be used before being
  78      *  assigned to, but is sometimes syntactically convenient.
  79      */
  80     ValueIterator() noexcept
  81         : internal() { }
  82
  83     /// Destructor.
  84     ~ValueIterator() {
  85         if (internal) decref();
  86     }
  87
  88     /// Return the value at the current position.
  89     std::string operator*() const;
  90
  91     /// Advance the iterator to the next position.
  92     ValueIterator & operator++();
  93
  94     /// Advance the iterator to the next position (postfix version).
  95     DerefWrapper_<std::string> operator++(int) {
  96         const std::string & value(**this);
  97         operator++();
  98         return DerefWrapper_<std::string>(value);
  99     }
 100
 101     /** Return the docid at the current position.
 102      *
 103      *  If we're iterating over values of a document, this method will throw
 104      *  Xapian::InvalidOperationError.
 105      */
 106     Xapian::docid get_docid() const;
 107
 108     /** Return the value slot number for the current position.
 109      *
 110      *  If the iterator is over all values in a slot, this returns that slot's
 111      *  number.  If the iterator is over the values in a particular document,
 112      *  it returns the number of each slot in turn.
 113      */
 114     Xapian::valueno get_valueno() const;
 115
 116     /** Advance the iterator to document id or value slot @a docid_or_slot.
 117      *
 118      *  If this iterator is over values in a document, then this method
 119      *  advances the iterator to value slot @a docid_or_slot, or the first slot
 120      *  after it if there is no value in slot @a slot.
 121      *
 122      *  If this iterator is over values in a particular slot, then this
 123      *  method advances the iterator to document id @a docid_or_slot, or the
 124      *  first document id after it if there is no value in the slot we're
 125      *  iterating over for document @a docid_or_slot.
 126      *
 127      *  Note: The "two-faced" nature of this method is due to how C++
 128      *  overloading works.  Xapian::docid and Xapian::valueno are both typedefs
 129      *  for the same unsigned integer type, so overloading can't distinguish
 130      *  them.
 131      *
 132      *  @param docid_or_slot    The docid/slot to advance to.
 133      */
 134     void skip_to(Xapian::docid docid_or_slot);
 135
 136     /** Check if the specified docid occurs.
 137      *
 138      *  The caller is required to ensure that the specified document id
 139      *  @a did actually exists in the database.
 140      *
 141      *  This method acts like skip_to() if that can be done at little extra
 142      *  cost, in which case it then returns true.  This is how
 143      *  glass databases behave because they store values in streams which allow
 144      *  for an efficient implementation of skip_to().
 145      *
 146      *  Otherwise it simply checks if a particular docid is present.  If it
 147      *  is, it returns true.  If it isn't, it returns false, and leaves the
 148      *  position unspecified (and hence the result of calling methods which
 149      *  depend on the current position, such as get_docid(), are also
 150      *  unspecified).  In this state, next() will advance to the first matching
 151      *  position after document @a did, and skip_to() will act as it would if
 152      *  the position was the first matching position after document @a did.
 153      *
 154      *  Currently the inmemory and remote backends behave in the
 155      *  latter way because they don't support streamed values and so skip_to()
 156      *  must check each document it skips over which is significantly slower.
 157      *
 158      *  @param docid    The document id to check.
 159      */
 160 #ifndef check
 161     bool check(Xapian::docid docid);
 162 #else
 163     // The AssertMacros.h header in the macOS SDK currently defines a check
 164     // macro.  Apple have deprecated check() in favour of __Check() and
 165     // plan to remove check() in a "future release", but for now prevent
 166     // expansion of check by adding parentheses in the method prototype:
 167     // https://www.opensource.apple.com/source/CarbonHeaders/CarbonHeaders-18.1/AssertMacros.h
 168     //
 169     // We do this conditionally, as these parentheses trip up SWIG's
 170     // parser:
 171     // https://github.com/swig/swig/issues/45
 172     bool (check)(Xapian::docid docid);
 173 #endif
 174
 175     /// Return a string describing this object.
 176     std::string get_description() const;
 177
 178     /** @private @internal ValueIterator is what the C++ STL calls an
 179      *  input_iterator.
 180      *
 181      *  The following typedefs allow std::iterator_traits<> to work so that
 182      *  this iterator can be used with the STL.
 183      *
 184      *  These are deliberately hidden from the Doxygen-generated docs, as the
 185      *  machinery here isn't interesting to API users.  They just need to know
 186      *  that Xapian iterator classes are compatible with the STL.
 187      */
 188     // @{
 189     /// @private
 190     typedef std::input_iterator_tag iterator_category;
 191     /// @private
 192     typedef std::string value_type;
 193     /// @private
 194     typedef Xapian::doccount_diff difference_type;
 195     /// @private
 196     typedef std::string * pointer;
 197     /// @private
 198     typedef std::string & reference;
 199     // @}
 200 };
 201
 202 /// Equality test for ValueIterator objects.
 203 inline bool
 204 operator==(const ValueIterator& a, const ValueIterator& b) noexcept
 205 {
 206     // Use a pointer comparison - this ensures both that (a == a) and correct
 207     // handling of end iterators (which we ensure have NULL internals).
 208     return a.internal == b.internal;
 209 }
 210
 211 /// Inequality test for ValueIterator objects.
 212 inline bool
 213 operator!=(const ValueIterator& a, const ValueIterator& b) noexcept
 214 {
 215     return !(a == b);
 216 }
 217
 218 }
 219
 220 #endif // XAPIAN_INCLUDED_VALUEITERATOR_H