roast/include/roast/lexical2/length.hpp

   1 //      Roast+ License
   2 /*
   3 */
   4 #ifndef __SFJP_ROAST__lexical2__length_HPP__
   5 #define __SFJP_ROAST__lexical2__length_HPP__
   6
   7 #include "roast/type_traits/is_derived.hpp"
   8
   9 namespace roast
  10 {
  11         namespace lexical
  12         {
  13                 //////////////////////////////////////////////////////////////////
  14
  15                 struct length_any {};   //      for convertible check by length_of<T>.
  16
  17                 template <unsigned int LENGTH>
  18                 struct length_ : length_any {
  19                         static const int length = LENGTH;
  20                 };
  21
  22                 typedef length_<0> zero_length;
  23
  24                 //////////////////////////////////
  25
  26                 template <typename U, bool _Valid>
  27                 struct _length_of_impl
  28                 {
  29                         static const int value = U::length;
  30                 };
  31                 template <typename U>
  32                 struct _length_of_impl<U, false>{};
  33
  34                 template <typename T>
  35                 struct length_of : public _length_of_impl<
  36                         T, type_traits::is_convertible<T,length_any>::value
  37                 > {};
  38
  39                 //////////////////////////////////////////////////////////////////
  40         }
  41 }
  42
  43 #endif//__SFJP_ROAST__lexical2__length_HPP__