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  1. #include <iostream>
  2. #include <typeinfo>
  3.  
  4. using namespace std;
  5.  
  6. template <typename T>
  7. class base {
  8. public:
  9.     base (T val = T())
  10.         : m_val(val)
  11.     {}
  12.     base (const base &other)
  13.         : base(other.m_val)
  14.     {}
  15.     virtual void base_specific_method()
  16.     {
  17.         cout << __func__ << " method called: " << m_val << endl;
  18.     }
  19.     void each_class_has_this() {
  20.         cout << __func__ << " this is boring..." << endl;
  21.     }
  22.     T m_val;
  23. };
  24. class other {
  25. public:
  26.     void each_class_has_this() {
  27.         cout << __func__ <<" this is boring..." << endl;
  28.     }
  29. };
  30. class derived_i : public base <int>
  31. {
  32. public:
  33.     derived_i () : base <int> (10)
  34.     {}
  35.     virtual void base_specific_method()
  36.     {
  37.         cout << __func__ <<" Hey! I'm interesting derived! And 10 == " << m_val << endl;
  38.     }
  39. };
  40.  
  41. template <typename T>
  42. class has_specific
  43. {
  44.     typedef char one;
  45.     typedef long two;
  46.  
  47.     template <typename C> static one test( typeof(&C::base_specific_method) ) ;
  48.     template <typename C> static two test(...);    
  49.  
  50. public:
  51.     enum { value = sizeof(test<T>(0)) == sizeof(char) };
  52. };
  53.  
  54. template <typename T>
  55. class caller {
  56. public:
  57.     caller (T val = T())
  58.         : m_val(val)
  59.     {}
  60.     void call() {
  61.         p_call(m_val);
  62.     }
  63. private:
  64.     template <typename T1=T>
  65.     typename enable_if<!has_specific<T1>::value,void>::type
  66.     p_call (T1 &val)
  67.     {
  68.         val.each_class_has_this();
  69.     }
  70.     template <typename T1=T>
  71.     typename enable_if<has_specific<T1>::value,void>::type
  72.     p_call (T1 &val)
  73.     {
  74.         val.base_specific_method();
  75.     }
  76. private:
  77.     T m_val;
  78. };
  79.  
  80. int main ()
  81. {
  82.     caller<other> c1;
  83.     caller<base<double> > c2;
  84.     caller<derived_i > c3;
  85.  
  86.     c1.call();
  87.     c2.call();
  88.     c3.call();
  89. }
Success #stdin #stdout 0s 3416KB
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stdin
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Standard input is empty
stdout
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each_class_has_this this is boring...
base_specific_method method called: 0
base_specific_method Hey! I'm interesting derived! And 10 == 10
https://ideone.com/bOYugL
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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