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  1. #include <iostream>
  2. #include <set>
  3. #include <sstream>
  4. #include <string>
  5.  
  6. // trying to resemble the OP
  7.  
  8. template <typename VALUE>
  9. class MultiAccessorT {
  10.   public:
  11.     typedef VALUE Value;
  12.     typedef std::set<Value> Table;
  13.   private:
  14.     Table &_tbl;
  15.   public:
  16.     MultiAccessorT(Table &tbl): _tbl(tbl) { }
  17.  
  18.     typename Table::iterator operator[](const std::string &str)
  19.     {
  20.       std::cout << "using operator[](const std::string&) ";
  21.       std::istringstream cvt(str);
  22.       Value value;
  23.       return cvt >> value ? _tbl.find(value) : _tbl.end();
  24.     }
  25.  
  26.     typename Table::iterator operator[](long value)
  27.     {
  28.       std::cout << "using operator[](long) ";
  29.       return _tbl.find((Value)value);
  30.     }
  31.  
  32.     typename Table::iterator operator[](double value)
  33.     {
  34.       std::cout << "using operator[](double) ";
  35.       return _tbl.find((Value)value);
  36.     }
  37.  
  38.     typename Table::iterator operator[](char value)
  39.     {
  40.       std::cout << "using operator[](char) ";
  41.       return _tbl.find((Value)value);
  42.     }
  43.  
  44.     // This resembles my personal "hair-killer":
  45.     typename Table::iterator operator[](bool value)
  46.     {
  47.       std::cout << "using operator[](bool) ";
  48.       return value ? _tbl.begin() : _tbl.end();
  49.     }
  50. };
  51.  
  52. // checking out
  53.  
  54. int main()
  55. {
  56.   // build some sample data
  57.   std::set<unsigned> tbl = { 0, 2, 4, 6, 8, 10, 12, 14 };
  58.   // template instance and instance
  59.   MultiAccessorT<unsigned> acc(tbl);
  60.   // test the operators
  61.   std::cout << "MultiAccessorT::operator[](const string&): ";
  62.   std::cout << (acc[std::string("6")] != tbl.end() ? "found." : "missed!") << std::endl;
  63.   std::cout << "MultiAccessorT::operator[](long): ";
  64.   std::cout << (acc[6L] != tbl.end() ? "found." : "missed!") << std::endl;
  65.   std::cout << "MultiAccessorT::operator[](double): ";
  66.   std::cout << (acc[6.0] != tbl.end() ? "found." : "missed!") << std::endl;
  67.   std::cout << "MultiAccessorT::operator[](char): ";
  68.   std::cout << (acc['\6'] != tbl.end() ? "found." : "missed!") << std::endl;
  69.   // examples which force conversion
  70.   std::cout << "using a constant string \"6\" (type const char[2]) ";
  71.   std::cout << (acc["6"] != tbl.end() ? "found." : "missed!") << std::endl;
  72.   /* FAILS:
  73.   std::cout << "using a int constant 6";
  74.   std::cout << (acc[6] != tbl.end() ? "found." : "missed!") << std::endl;
  75.   g++ error: ambiguous overload for 'operator[]' (operand types are 'MultiAccessorT<unsigned int>' and 'int')
  76.   Found candidates are:
  77.      typename Table::iterator operator[](long value)
  78.      typename Table::iterator operator[](double value)
  79.      typename Table::iterator operator[](char value)
  80.    */
  81.   // done
  82.   return 0;
  83. }
Success #stdin #stdout 0s 4348KB
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Standard input is empty
stdout
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MultiAccessorT::operator[](const string&): using operator[](const std::string&) found.
MultiAccessorT::operator[](long): using operator[](long) found.
MultiAccessorT::operator[](double): using operator[](double) found.
MultiAccessorT::operator[](char): using operator[](char) found.
using a constant string "6" (type const char[2]) using operator[](bool) found.
https://ideone.com/dsb3Da
language:
C++ (gcc 8.3)
created:
7 years ago
visibility:
public

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