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  1. #include <iostream>
  2. #include <utility>
  3. #include <map>
  4. #include <string>
  5. #include <initializer_list>
  6. #include <cstring>
  7. #include <stdexcept>
  8.  
  9. namespace LiteralSwitch {
  10.  
  11. // simple hash function
  12. constexpr unsigned int dbj2Hash(const char* str, size_t size, int index = 0)
  13. {
  14.     return !str[index] ? 0x1505 : (dbj2Hash(str, size, index + 1) * 0x21) ^ str[index];
  15. }
  16.  
  17.  
  18. // Create a literal type for short-hand case strings
  19. constexpr unsigned int operator"" _C ( const char str[], size_t size)
  20. {
  21.     return dbj2Hash(str, size - 1);
  22. }
  23.  
  24.  
  25. struct CaseLabel
  26. {
  27.     typedef const char* label_type;
  28.     typedef uint32_t    value_type;
  29.     typedef std::pair<const label_type, value_type>  store_type;
  30.  
  31.     constexpr CaseLabel(const char* str)
  32.         :   data_(std::make_pair(str, dbj2Hash(str, strlen(str))))
  33.     {
  34.     }
  35.  
  36.     constexpr operator value_type() const { return data_.second; }
  37.     constexpr operator label_type() const { return data_.first; }
  38.     constexpr operator store_type() const { return data_; }
  39.  
  40. private:
  41.  
  42.     const store_type data_;
  43. };
  44. struct  compare {
  45.     bool operator()(const char *left, const char *right) const
  46.     {
  47.         return strcmp(left, right) < 0;
  48.     }
  49. };
  50.  
  51. struct CaseLabelSet
  52.         : private std::map<CaseLabel::label_type, CaseLabel::value_type, compare>
  53. {
  54.     CaseLabelSet(std::initializer_list<CaseLabel> values)
  55.     {
  56.         for(auto x : values) insert(x);
  57.     }
  58.  
  59.     CaseLabel::value_type operator()(const std::string& label) const
  60.     {
  61.         return operator()(label.c_str());
  62.     }
  63.     CaseLabel::value_type operator()(const char* label) const
  64.     {
  65.         auto it = find(label);
  66.         if(it == end())
  67.         {
  68.             throw std::invalid_argument("Case label not found");
  69.         }
  70.  
  71.         return it->second;
  72.     }
  73. };
  74.  
  75. }
  76.  
  77. using namespace LiteralSwitch;
  78.  
  79. void Test(const std::string& cond)
  80. {
  81.     static const CaseLabelSet setValues = {"Hello", "World"};
  82.  
  83.     try
  84.     {
  85.         switch(setValues(cond))
  86.         {
  87.         case "Hello"_C: std::cout << "Goodbye"; break;
  88.         case "World"_C: std::cout << "Planet"; break;
  89.         default: std::cout << "BOGUS!";
  90.  
  91.         }
  92.         std::cout << std::endl;
  93.     }
  94.     catch(std::invalid_argument)
  95.     {
  96.         std::cout << "exception on unknown switch/case value. should go to default" << std::endl;
  97.     }
  98. }
  99.  
  100.  
  101. int main()
  102. {
  103.     Test("Hello");
  104.     Test("World");
  105.     Test("hello");
  106. }
  107.  
Success #stdin #stdout 0s 2988KB
comments (?)
stdin
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Standard input is empty
stdout
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Goodbye
Planet
exception on unknown switch/case value. should go to default
https://ideone.com/sL3txv
Strings in case labels with switch condition validation
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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