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

   1 [#currying]
   2 [section Currying]
   3
   4 A [link metafunction template metafunction] supports ['currying] when it accepts
   5 less arguments than it normally expects. When less arguments are provided, then
   6 it returns a [link metafunction_class template metafunction class] expecting
   7 the remaining arguments. That template metafunction class is also expected to
   8 support currying.
   9
  10 For example assuming the following metafunction is given:
  11
  12   template <class A, class B>
  13   struct plus;
  14
  15 It takes two values, adds them and returns their result. For example:
  16
  17   static_assert(
  18     plus<
  19       std::integral_constant<int, 11>,
  20       std::integral_constant<int, 2>
  21     >::type::value == 13,
  22     "This should work"
  23   );
  24
  25 If it supports currying, then the following should also work:
  26
  27   using inc = plus<std::integral_constant<int, 1>>;
  28
  29   static_assert(
  30     inc::apply<std::integral_constant<int, 12>>::type::value == 13,
  31     "This should work"
  32   );
  33
  34 The above example defines the `inc` template metafunction class by calling
  35 `plus` with just one argument: the [link boxed_value boxed] `1` value.
  36
  37 [endsect]
  38