ceph/src/boost/libs/metaparse/doc/nullary_metafunction.qbk

   1 [#nullary_metafunction]
   2 [section Nullary template metafunction]
   3
   4 A ['nullary template metafuncion] is a [link metafunction template metafunction]
   5 taking 0 arguments. It is a type with a nested type called `type`, which is the
   6 return value of the nullary metafunction. For example:
   7
   8   struct always13
   9   {
  10     using type = std::integral_constant<int, 13>;
  11   };
  12
  13 This metafunction is called `always13`. It is a nullary metafunction, because it
  14 takes no arguments. It always returns `std::integral_constant<int, 13>`.
  15
  16 To call this metafunction, one has to access its `::type`. For example:
  17
  18   always13::type
  19
  20 The above example calls the metafunction to get
  21 `std::integral_constant<int, 13>`.
  22
  23 [endsect]
  24