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  1. #include <cstddef>
  2. #include <utility>
  3.  
  4. 	template<std::size_t X>
  5. 	struct line_t { enum{value=X}; constexpr line_t(){} };
  6.  
  7. 	template<std::size_t line, char c>
  8. 	constexpr std::integral_constant<bool, false> use_flag(
  9. 	  std::integral_constant<char,c>, line_t<line>
  10. 	) { return {}; }
  11.  
  12. 	#define FLAG_USE( C ) \
  13. 	constexpr std::integral_constant<bool, true> use_flag( \
  14. 	  std::integral_constant<char,C>, line_t<__LINE__> \
  15. 	) { return {}; }
  16.  
  17. 	template<char c, std::size_t line>
  18. 	constexpr std::size_t count_uses( line_t<line> from, line_t<1> length ){
  19. 	  return use_flag( std::integral_constant<char, c>{}, from )();
  20. 	}
  21. 	template<char c, std::size_t line>
  22. 	constexpr std::size_t count_uses( line_t<line> from, line_t<0> length ){
  23. 	  return 0;
  24. 	}
  25.  
  26. 	template<char c, std::size_t f, std::size_t l>
  27. 	constexpr std::size_t count_uses(line_t<f> from, line_t<l> length ){
  28. 	  return count_uses<c>( from, line_t< l/2 >{} )+ count_uses<c>( line_t< f+l/2>{}, line_t<(l+1)/2>{} );
  29. 	}
  30.  
  31. 	#define UNIQUE(C) \
  32. 	  FLAG_USE(C) \
  33. 	  static_assert( count_uses<C>( line_t<0>{}, line_t<__LINE__+1>{} )==1, "too many" )
  34.  
  35. UNIQUE('a');
  36. UNIQUE('b');
  37. UNIQUE('c');
  38. UNIQUE('a');
  39.  
  40. int main() {}
Compilation error #stdin compilation error #stdout 0s 15240KB
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stdin
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Standard input is empty
compilation info 
prog.cpp:33:4: error: static assertion failed: too many
    static_assert( count_uses<C>( line_t<0>{}, line_t<__LINE__+1>{} )==1, "too many" )
    ^
prog.cpp:38:1: note: in expansion of macro ‘UNIQUE’
 UNIQUE('a');
 ^~~~~~
stdout
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Standard output is empty
https://ideone.com/ZGmHOs
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
secret

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