cast not needing to perform a run

This question already has an answer here:

When should static_cast, dynamic_cast, const_cast and reinterpret_cast be used? 6 answers

---

class Base {
public:
    virtual ~Base() {}
    // ...
};

class Derived : public Base {
    // ...
};

"Typical use":

void foo(Derived*);

void f(Base* pb)
{
    if (Derived* pd = dynamic_cast<Derived*>(pb)) {
        foo(pd);
    }
}

"Above quote":

void bar(Base*);

void f(Derived* pd)
{
    Base* pb = dynamic_cast<Base*>(pd); // the dynamic_cast is useless here
                                        //  because a Derived IS-A Base, always
    bar(pb); // Note: could as well call directly bar(pd); (implicit conversion)
}

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dynamic_cast is mostly used for downcast and cross-cast. The gotcha mentions upcast.

Having structs B1, B2, D:B1, B2:

upcast: D* -> B1*, D* -> B2*

downcast: D* <- B1*, D* <- B2*

cross-cast: B1* <-> B2* (will work if your most derived class is D).

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