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  1. #include <string>
  2. #include <stdexcept>
  3. #include <iostream>
  4.  
  5. template <class T>        
  6. struct ConstrainedText {        
  7.   std::string m;                 
  8.  
  9. protected:
  10.   ConstrainedText() {}
  11.   ~ConstrainedText() {}
  12. public: 
  13.   bool is_valid() {        
  14.     return T::is_valid_string(m);        
  15.   }        
  16.  
  17.   static T Create(std::string const & s)
  18.   {
  19.       if (T::is_valid_string(s)) {
  20.           T t;
  21.           static_cast<ConstrainedText<T>&>(t).m = s;
  22.           return t;
  23.       }
  24.  
  25.       throw std::runtime_error("invalid input!");
  26.   }
  27. };        
  28.  
  29. struct Angle : public ConstrainedText<Angle> {        
  30.    static bool is_valid_string( std::string s ) {         
  31.       return s == "deg" || s=="rad";        
  32.    }          
  33. };        
  34.  
  35.  
  36. struct Length : public ConstrainedText<Length> {        
  37.    static bool is_valid_string( std::string s ) {         
  38.       return s == "mm" || s == "m" || s == "ft" || s == "in";        
  39.    }          
  40. };        
  41.  
  42. int main()
  43. {
  44.    auto a = Angle::Create("deg");
  45.    auto l = Length::Create("mm");
  46.  
  47.    try {
  48.        Angle::Create("bimbo");
  49.    } catch (std::runtime_error & pEx) {
  50.        std::cout << "exception as expected" << std::endl;
  51.    }
  52.  
  53.    try {
  54.        Length::Create("bimbo");
  55.    } catch (std::runtime_error & pEx) {
  56.        std::cout << "exception as expected" << std::endl;
  57.    }
  58. }
Success #stdin #stdout 0s 3020KB
comments (?)
stdin
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Standard input is empty
stdout
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exception as expected
exception as expected
https://ideone.com/EP5C4
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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