[boost] [utility] Proposal of a utility component

From: Wang Weiwei (wwwang_at_[hidden])
Date: 2006-02-03 22:17:39

Hello boosters,

I have a tiny component I hope it can attact any interst. It is one step forward of the built-in interpert_cast operator, a force_cast free function:

template <typename destination_type, typename source_type>
destination_type force_cast(source_type s)
{
        union 
        {
                source_type s;
                destination_type d;
        } u;
        u.s = s;
        return u.d;
}

Demonstration of use: The following code is to demonstrate a pointer to non-virtual function is actualy a normal function pointer:

class Shape
{
public:
        virtual void Move(void) const=0;
        virtual void Draw(void) const=0;
        void Nonvirtual(void) const 
        { std::cout << "Calling Shape::Nonvirtual(void)" << std::endl; }
};

class Triangle : public Shape
{
public:
        virtual void Move(void) const {}
        virtual void Draw(void) const {}
        virtual void DrawTriangle(void) const {}
};

        typedef void (Shape::*pmfb_t)(void) const;
        pmfb_t pmfb_n = &Shape::Nonvirtual;
        
        Triangle tri;
        (tri.*pmfb_n)(); 													  	   // 1                                 	
        (force_cast<void (*)(Shape *)>(pmfb_n))(static_cast<Shape *>(&tri));	   // 2
        
        // or in a clearer manner
        typedef void (*pf_t)(Shape *);
        (force_cast<pf_t>(pmfb_n))(static_cast<Shape *>(&tri));                    // 3

The output is:
Calling Shape::Nonvirtual(void)			// from 1
Calling Shape::Nonvirtual(void)   		// from 2
Calling Shape::Nonvirtual(void)     	// from 3

Wang Weiwei