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

   1 [#digit_to_int]
   2 [section digit_to_int]
   3
   4 [h1 Synopsis]
   5
   6   namespace util
   7   {
   8     template <class D>
   9     struct digit_to_int;
  10   }
  11
  12 This is a [link lazy_metafunction lazy template metafunction] that supports
  13 [link currying currying].
  14
  15 [table Arguments
  16   [[Name] [Type]]
  17   [[`D`]  [[link boxed_value boxed] character value]]
  18 ]
  19
  20 [h1 Description]
  21
  22 Converts a boxed character containing a value in the range `['0'..'9']` to an
  23 integer.
  24
  25 [h1 Return value]
  26
  27 It returns a [link boxed_value boxed] integer value.
  28
  29 [h1 Header]
  30
  31   #include <boost/metaparse/util/digit_to_int.hpp>
  32
  33 [h1 Expression semantics]
  34
  35 For any `C` boxed character value in the range `['0'..'9']` the following
  36 expressions are equivalent
  37
  38   digit_to_int<>::apply<C>::type
  39   digit_to_int<C>::type
  40   digit_to_int_c<C::type::value>::type
  41
  42 [h1 Example]
  43
  44   #include <boost/metaparse/util/digit_to_int.hpp>
  45
  46   #include <type_traits>
  47
  48   using namespace boost::metaparse;
  49
  50   struct nullary_metafunction_returning_4
  51   {
  52     using type = std::integral_constant<char, '4'>;
  53   };
  54
  55   static_assert(
  56     util::digit_to_int<std::integral_constant<char, '0'>>::type::value == 0,
  57     "it should convert a character to the corresponding integer value"
  58   );
  59
  60   static_assert(
  61     util::digit_to_int<>::type
  62       ::apply<std::integral_constant<char, '7'>>::type::value == 7,
  63     "it should support currying"
  64   );
  65
  66   static_assert(
  67     util::digit_to_int<nullary_metafunction_returning_4>::type::value == 4,
  68     "it should support lazy evaluation"
  69   );
  70
  71 [endsect]
  72