fork(2) download
copy 
  1. #include <cstddef>
  2. #include <utility>
  3. #include <string>
  4. #include <map>
  5.  
  6. enum TestEnum {
  7.    BeginVal = 0,
  8.    One = BeginVal,
  9.    Two,
  10.    Three,
  11.    EndVal
  12. };
  13.  
  14. template<TestEnum e>
  15. struct MapEntry {
  16.   enum { val = e };
  17.   std::string s;
  18.   MapEntry( std::string s_ ):s(s_) {}
  19. };
  20.  
  21. void do_in_order() {}
  22. template<typename F0, typename... Fs>
  23. void do_in_order(F0&& f0, Fs&&... fs) {
  24.   std::forward<F0>(f0)();
  25.   do_in_order( std::forward<Fs>(fs)... );
  26. }
  27.  
  28. template<typename... MapEntries>
  29. struct count_entries:std::integral_constant< std::size_t, sizeof...(MapEntries) > {};
  30.  
  31. // should also detect duplicates and check the range of the values:
  32. template<typename... MapEntries>
  33. struct caught_them_all:
  34.     std::integral_constant<
  35. 		bool,
  36. 		count_entries<MapEntries...>::value == (TestEnum::EndVal-TestEnum::BeginVal)
  37. 	>
  38. {};
  39.  
  40. struct BuildMap {
  41.   typedef std::map<std::string, TestEnum> result_map;
  42.   mutable result_map val;
  43.   operator result_map() const {
  44.     return std::move(val);
  45.   }
  46.   template<typename... MapEntries>
  47.   BuildMap( MapEntries&&... entries ) {
  48.     static_assert( caught_them_all<MapEntries...>::value, "Missing enum value" );
  49.     bool _[] = { ( (val[ entries.s ] = TestEnum(MapEntries::val)), false )... };
  50.   }
  51. };
  52.  
  53. std::map< std::string, TestEnum > bob = BuildMap(
  54. 	MapEntry<One>("One")
  55. 	,MapEntry<Two>("Two")
  56. #if 0
  57. 	,MapEntry<Three>("Three")
  58. #endif
  59. );
  60.  
  61. int main() {}
  62.  
  63.  
Compilation error #stdin compilation error #stdout 0s 0KB
comments (?)
stdin
copy 
Standard input is empty
compilation info 
prog.cpp: In instantiation of ‘BuildMap::BuildMap(MapEntries&& ...) [with MapEntries = {MapEntry<(TestEnum)0u>, MapEntry<(TestEnum)1u>}]’:
prog.cpp:59:1:   required from here
prog.cpp:48:5: error: static assertion failed: Missing enum value
prog.cpp:49:10: warning: unused variable ‘_’ [-Wunused-variable]
stdout
copy 
Standard output is empty
https://ideone.com/V9Knqr
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!