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  1. #include <iostream>
  2. #include <string>
  3. #include <map>
  4.  
  5. template <typename T>
  6. struct GenKeyTypeOrder;
  7.  
  8.  
  9. class GenKeyImplInt {
  10. public:
  11.    // true if before other Key in other 
  12.    virtual bool before(const GenKeyImplInt&) const = 0;
  13.    // type value
  14.    virtual int typeOrder() const = 0;
  15.  
  16.    virtual GenKeyImplInt* clone() const = 0;
  17.    virtual ~GenKeyImplInt() {}
  18.  
  19.    virtual void print(std::ostream& os) const = 0;
  20. };
  21.  
  22. template <typename RealKey>
  23. class GenKeyImpl : public GenKeyImplInt {
  24. public:
  25.    GenKeyImpl(RealKey realKey) : realKey(realKey) {}
  26.    // true if before other Key in other 
  27.    virtual bool before(const GenKeyImplInt& r) const 
  28.    { 
  29.       const GenKeyImpl* rp = dynamic_cast<const GenKeyImpl*>(&r);
  30.       if (rp) return realKey < rp->realKey;
  31.       return typeOrder() < r.typeOrder();
  32.    }
  33.    // type value
  34.    virtual int typeOrder() const { return GenKeyTypeOrder<RealKey>::VALUE; }
  35.  
  36.    virtual GenKeyImpl* clone() const { return new GenKeyImpl(*this); }
  37.    virtual void print(std::ostream& os) const { os << realKey; }
  38. private:
  39.    RealKey realKey;
  40. };
  41.  
  42. class GenKey {
  43. public:
  44.    // true if before other Key in other 
  45.    friend bool operator < (const GenKey& l, const GenKey& r) 
  46.    {
  47.        return l.impl->before(*r.impl);
  48.    }
  49.    template <typename T>
  50.    GenKey(T t) : impl(new GenKeyImpl<T>(t)) {}
  51.    GenKey(const GenKey& oth) : impl(oth.impl->clone()) {}
  52.    ~GenKey() { delete impl; }
  53. private:
  54.    GenKey& operator = (const GenKey& oth); // not defined
  55.    GenKeyImplInt* impl;
  56.  
  57.    friend std::ostream& operator << (std::ostream& os, const GenKey& obj) 
  58.    {
  59.        obj.impl->print(os);
  60.        return os;
  61.    }
  62. };
  63.  
  64.  
  65. // define for every type you want be used as generic key
  66. template <>
  67. struct GenKeyTypeOrder<int> { enum { VALUE = 0 }; };
  68. template <>
  69. struct GenKeyTypeOrder<std::string> { enum { VALUE = 1 }; };
  70.  
  71.  
  72. int main() {
  73.   std::map<GenKey, int> genMap;
  74.   genMap[std::string("ala")] = 7;
  75.   genMap[1] = 8;
  76.  
  77.   for (std::map<GenKey, int>::iterator it = genMap.begin(); it != genMap.end(); ++it)
  78.      std::cout << it->first << "-->" << it->second << "\n"; 
  79.  
  80. }
Success #stdin #stdout 0s 3064KB
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stdin
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Standard input is empty
stdout
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1-->8
ala-->7
https://ideone.com/gCaEZ
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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