demo, C++ (clang) - rextester

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#include <iostream>
#include <type_traits>

using namespace std;

template <typename T>
class Base{
public:
    Base(){}
    virtual void print() const {cout<<"Base class"<<endl;}
};

template <typename T>
class Derived :public Base<T>{
public:
    Derived() {}
    void print() const {cout<<"Derived class"<<endl;}
};

template <typename T>
class Derived2 {
public:
    Derived2() {}
    void print() const {cout<<"Derived2 class"<<endl;}
};

class Derived3 {
public:
    Derived3() {}
    void print() const {cout<<"Derived3 class"<<endl;}
};

template <typename T>
void func(T x){    // <----- Why is function is called?
    x.print();
    cout<<"in func(T)"<<endl;
}

template <typename T, template <typename> class D>
typename std::enable_if<std::is_base_of<Base<T>,D<T>>::value>::type
func(const D<T>& x){
    x.print();
    cout<<"in func(Base<T>)"<<endl;
}

int main () {
    Base<int> b;
    func(b);
    Derived<int> d;
    func(d);
    Base<int>& rb = d;
    func(rb);
   
    Derived2<int> d2;
    Derived3 d3;
    func(d2);
    func(d3);
    return 0;
}

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Compilation time: 0.62 sec, absolute running time: 0.14 sec, cpu time: 0 sec, memory peak: 3 Mb, absolute service time: 0,77 sec