See the code below.
a) Does, in this case (simple inheritance, no virtual members), the static cast in B::df() have any overhead (whatsoever)? I found some conflicting answers to similar questions, that's why I am asking...
b) I was thinking about making const M1 * func
private in A and introducing a new private field const M2 * func
into B to avoid the cast, but it kind of complicates things up and makes use of smart pointers more difficult. Do you see a better way to avoid the cast?
class M1 {
public:
double f() const;
};
class M2 : public M1 { public: double df() const; };
class A { protected: const M1 * func; public: A(const M1 * p); ~A(); double f() const; };
class B : public A { public: B(const M2 * p); double df() const; };
double M1::f() const { return 1973.0; }
double M2::df() const { return 0.0; }
A::~A() { delete func; } A::A(const M1 * p) : func(p) {} double A::f() const { return func->f(); }
B::B(const M2 * p) : A(p) {} double B::df() const { return static_cast<const M2*>(func)->df(); }
static_cast<T>(e)
is equivalent to creating an invented temporary variable v in the following way:
T v(e); //where T is an arbitrary type and e is an arbitrary expression.
The runtime cost of a static_cast is exactly the cost of the above statement