xapian-core/include/xapian/valueiterator.h

   1 /** @file  valueiterator.h
   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     /** Default constructor.
  60      *
  61      *  Creates an uninitialised iterator, which can't be used before being
  62      *  assigned to, but is sometimes syntactically convenient.
  63      */
  64     XAPIAN_NOTHROW(ValueIterator())
  65         : internal(0) { }
  66
  67     /// Destructor.
  68     ~ValueIterator() {
  69         if (internal) decref();
  70     }
  71
  72     /// Return the value at the current position.
  73     std::string operator*() const;
  74
  75     /// Advance the iterator to the next position.
  76     ValueIterator & operator++();
  77
  78     /// Advance the iterator to the next position (postfix version).
  79     DerefWrapper_<std::string> operator++(int) {
  80         const std::string & value(**this);
  81         operator++();
  82         return DerefWrapper_<std::string>(value);
  83     }
  84
  85     /** Return the docid at the current position.
  86      *
  87      *  If we're iterating over values of a document, this method will throw
  88      *  Xapian::InvalidOperationError.
  89      */
  90     Xapian::docid get_docid() const;
  91
  92     /** Return the value slot number for the current position.
  93      *
  94      *  If the iterator is over all values in a slot, this returns that slot's
  95      *  number.  If the iterator is over the values in a particular document,
  96      *  it returns the number of each slot in turn.
  97      */
  98     Xapian::valueno get_valueno() const;
  99
 100     /** Advance the iterator to document id or value slot @a docid_or_slot.
 101      *
 102      *  If this iterator is over values in a document, then this method
 103      *  advances the iterator to value slot @a docid_or_slot, or the first slot
 104      *  after it if there is no value in slot @a slot.
 105      *
 106      *  If this iterator is over values in a particular slot, then this
 107      *  method advances the iterator to document id @a docid_or_slot, or the
 108      *  first document id after it if there is no value in the slot we're
 109      *  iterating over for document @a docid_or_slot.
 110      *
 111      *  Note: The "two-faced" nature of this method is due to how C++
 112      *  overloading works.  Xapian::docid and Xapian::valueno are both typedefs
 113      *  for the same unsigned integer type, so overloading can't distinguish
 114      *  them.
 115      *
 116      *  @param docid_or_slot    The docid/slot to advance to.
 117      */
 118     void skip_to(Xapian::docid docid_or_slot);
 119
 120     /** Check if the specified docid occurs.
 121      *
 122      *  The caller is required to ensure that the specified document id
 123      *  @a did actually exists in the database.
 124      *
 125      *  This method acts like skip_to() if that can be done at little extra
 126      *  cost, in which case it then returns true.  This is how
 127      *  glass databases behave because they store values in streams which allow
 128      *  for an efficient implementation of skip_to().
 129      *
 130      *  Otherwise it simply checks if a particular docid is present.  If it
 131      *  is, it returns true.  If it isn't, it returns false, and leaves the
 132      *  position unspecified (and hence the result of calling methods which
 133      *  depend on the current position, such as get_docid(), are also
 134      *  unspecified).  In this state, next() will advance to the first matching
 135      *  position after document @a did, and skip_to() will act as it would if
 136      *  the position was the first matching position after document @a did.
 137      *
 138      *  Currently the inmemory and remote backends behave in the
 139      *  latter way because they don't support streamed values and so skip_to()
 140      *  must check each document it skips over which is significantly slower.
 141      *
 142      *  @param docid    The document id to check.
 143      */
 144 #ifndef check
 145     bool check(Xapian::docid docid);
 146 #else
 147     // The AssertMacros.h header in the OS X SDK currently defines a check
 148     // macro.  Apple have deprecated check() in favour of __Check() and
 149     // plan to remove check() in a "future release", but for now prevent
 150     // expansion of check by adding parentheses in the method prototype:
 151     // http://www.opensource.apple.com/source/CarbonHeaders/CarbonHeaders-18.1/AssertMacros.h
 152     //
 153     // We do this conditionally, as these parentheses trip up SWIG's
 154     // parser:
 155     // https://github.com/swig/swig/issues/45
 156     bool (check)(Xapian::docid docid);
 157 #endif
 158
 159     /// Return a string describing this object.
 160     std::string get_description() const;
 161
 162     /** @private @internal ValueIterator is what the C++ STL calls an
 163      *  input_iterator.
 164      *
 165      *  The following typedefs allow std::iterator_traits<> to work so that
 166      *  this iterator can be used with the STL.
 167      *
 168      *  These are deliberately hidden from the Doxygen-generated docs, as the
 169      *  machinery here isn't interesting to API users.  They just need to know
 170      *  that Xapian iterator classes are compatible with the STL.
 171      */
 172     // @{
 173     /// @private
 174     typedef std::input_iterator_tag iterator_category;
 175     /// @private
 176     typedef std::string value_type;
 177     /// @private
 178     typedef Xapian::doccount_diff difference_type;
 179     /// @private
 180     typedef std::string * pointer;
 181     /// @private
 182     typedef std::string & reference;
 183     // @}
 184 };
 185
 186 bool
 187 XAPIAN_NOTHROW(operator==(const ValueIterator &a, const ValueIterator &b));
 188
 189 /// Equality test for ValueIterator objects.
 190 inline bool
 191 operator==(const ValueIterator &a, const ValueIterator &b) XAPIAN_NOEXCEPT
 192 {
 193     // Use a pointer comparison - this ensures both that (a == a) and correct
 194     // handling of end iterators (which we ensure have NULL internals).
 195     return a.internal == b.internal;
 196 }
 197
 198 bool
 199 XAPIAN_NOTHROW(operator!=(const ValueIterator &a, const ValueIterator &b));
 200
 201 /// Inequality test for ValueIterator objects.
 202 inline bool
 203 operator!=(const ValueIterator &a, const ValueIterator &b) XAPIAN_NOEXCEPT
 204 {
 205     return !(a == b);
 206 }
 207
 208 }
 209
 210 #endif // XAPIAN_INCLUDED_VALUEITERATOR_H