compiler_explorer/211206_polymorphism1.cpp at master · nglee/compiler_explorer · GitHub

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#include <cstdio>

class Base
{
public:
    Base() = default;

    const char* name = "Base";

    Base(const Base& rhs) { puts("Base copy const."); }
};

class Derived : public Base
{
public:
    Derived() = default;

    const char* name = "Derived";
};

void f1(Base b)
{
    puts(b.name);
}

void f2(Base& rb)
{
    puts(rb.name);
    puts(static_cast<Derived&>(rb).name);
}

void f3(const Base& crb)
{
    puts(crb.name);
    puts(static_cast<const Derived&>(crb).name);
}

void f4(Base* pb)
{
    puts(pb->name);
    puts(static_cast<Derived*>(pb)->name);
    // compiler error: cannot 'dynamic_cast' 'pb' (of type 'class Base*') to type 'class Derived*' (source type is not polymorphic)
    // puts(dynamic_cast<Derived*>(pb)->name);
    //      ^~~~~~~~~~~~~~~~~~~~~~~~~~
    // add virtual destructor to Base then it compiles
}

void f5(Base* const cpb)
{
    puts(cpb->name);
    puts(static_cast<Derived* const>(cpb)->name);
    puts(static_cast<Derived*>(cpb)->name); // OK
}

void f6(const Base* pcb)
{
    puts(pcb->name);
    puts(static_cast<const Derived*>(pcb)->name);
    // compiler error: 'static_cast' from type 'const Base*' to type 'Derived*' casts away quialifiers
    // puts(static_cast<Derived*>(pcb)->name); // NOT OK
    //
}

void f7(const Base* const cpcb)
{
    puts(cpcb->name);
    puts(static_cast<const Derived*>(cpcb)->name); // OK
    puts(static_cast<const Derived* const>(cpcb)->name); // OK
}

int main()
{
    Derived d;

    f1(d);
    f2(d);
    f3(d);
    f4(&d);
    f5(&d);
    f6(&d);
    f7(&d);
}

// Output:
// Base copy const.
// Base
// Base
// Derived
// Base
// Derived
// Base
// Derived
// Base
// Derived
// Derived
// Base
// Derived
// Base
// Derived
// Derived