Приведение производного типа к предку

class Inherit : public Base
{
public:
   int c;
   Inherit(int a, b, _c)
   : Base(a, b), c(_c)
   {}
};

template <typename T>
void foo( T & t ) {
    static_assert( std::is_base_of<Base, T>::value, "T is not derived from Base" );
    ...
}

#include <iostream>
 
struct A {
    virtual void foo() { std::cout << "A::foo()\n"; }
};
 
struct B : A {
    void foo() { std::cout << "B::foo()\n"; }
};
 
struct C {
    void foo() { std::cout << "C::foo()\n"; }
};
 
void bar( A & a ) {
    a.foo();
}
 
int main() {
    A a;
    B b;
    C c;
    bar( a );
    bar( b );
    //bar( c ); // fail
}

class Base{
   public:
    virtual void out(){
        cout<<"base"<<endl;
    }
};
class Derived:public Base{
public:
    virtual void out(){
        cout<<"derived"<<endl;
    }
};
 
int main()
{
    Base a;
    Base *pa;
    Derived d;
    a = d;
    pa = &d;
    a.out();
    pa->out();
 
    return 0;
}

 Base &ba = d;
    ba.out();

class Base{
* *public:
* * virtual void out(){
* * * * cout<<"base"<<endl;
* * }
};
class Derived:public Base{
public:
* * virtual void out(){
* * * * cout<<"derived"<<endl;
* * }
};
int main()
{
* * Base a;
* * Base *pa;
* * Derived d;
* * a = d;           //<--- срезка
* * pa = &d;
* * a.out();
* * pa->out();
return 0;
}

class Base{
   public:
    virtual void out(){
        cout<<"base"<<endl;
    }
};
class Derived:public Base{
public:
    virtual void out(){
        cout<<"derived"<<endl;
    }
};
 
int main()
{
    Derived d;
    Base& a = d;
    a.out();
}