read_write_lock_acc, C++ (gcc)

read_write_lock_acc

#include <iostream>
#include <algorithm>

struct AB 
{
	int x = 1;
	double y = 100.;
};

typedef int read_lock;
typedef double write_lock;

template<typename LockType, typename ABType>
class X : public ABType{
public:
    typedef const ABType& access_type;
};

template<typename ABType>
class X<write_lock, ABType> : public ABType{
public:
    typedef ABType& access_type;
};

template<typename LockType>
struct XY:protected X<LockType, AB>{

template<typename WeightType>
	std::enable_if_t<std::is_floating_point<WeightType>::value, WeightType> value() const
	{
		return (WeightType)X<LockType, AB>::y;
	}

template<typename WeightType>
	std::enable_if_t<std::is_integral<WeightType>::value, WeightType> value() const
	{
		return X<LockType, AB>::x;
	}
    
    typedef typename X<LockType, AB>::access_type access_type;
    
    operator access_type(){
        return *this;
    }
    
    access_type data(){
        return *this;
    }
    
    template<typename T = LockType>
        std::enable_if_t<std::is_same<T, read_lock>::value, const AB&> data(){return *this;}   
    
    template<typename T = LockType>
        std::enable_if_t<std::is_same<T, write_lock>::value, AB&> data(){return *this;}

};

int main(int, char**) {

XY<write_lock> xy;
	std::cout << xy.value<float>() << std::endl
		<< xy.value<short>() << std::endl;
      
    
     // AB& ab0 = xy; // <---------- why error here?
	
    // const AB& ab1 = xy.data();
    AB& ab1 = xy.data();
    
    AB& ab2 = xy.data<>();
   
    
	return 0;
}


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