Policy based smart pointer, C++ (gcc)

Policy based smart pointer

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//Title of this code

#include <iostream>
#include <stdexcept>

template<typename T>
struct FullCheckPolicy
{
    static void Check(T *_p)
    {
        if (!_p)
        {
            throw std::runtime_error("Null pointer!");
        }
    }
};
    
template<typename T>
struct NoCheckPolicy
{
    static void Check(T *_p)
    {
        
    }
};

template<typename T, 
    template<typename E>
    class CheckingPolicy = NoCheckPolicy>
class SmartPtr
{
private:
    T *p_;
    
public:
    const T * getPtr() const
    {
        CheckingPolicy<T>::Check(p_);
        
        return p_;
    }
    
    T * getPtr() 
    {
        CheckingPolicy<T>::Check(p_);
        
        return p_;
    }
    
public:
    SmartPtr(T *p = NULL) : p_(p)
    {
    }
    
    template<
        template <typename F> class ChkPolicy>
    SmartPtr(const SmartPtr<T, ChkPolicy> &_ptr)
    {
        p_ = const_cast<T*>(_ptr.p_);
    }
    
    template<
        template <typename F> class ChkPolicy>
    SmartPtr & operator = (const SmartPtr<T, ChkPolicy> &_other)
    {
        p_ = const_cast<T*>(_other.p_);
    }
    
    const T * operator ->() const
    {
        return this->getPtr();
    }
    
    T * operator ->()
    {
        return this->getPtr();
    }
    
    const T & operator *() const
    {
     
        return this->getPtr();
    }
    
    T & operator *()
    {
        return *this->getPtr();
    }
};
    
template<typename T>
SmartPtr<T> make_smart(const T &val)
{
    SmartPtr<T> ptr = new T(val);
    
    return ptr;
}

int main()
{
    SmartPtr<int, FullCheckPolicy> ptr;
    SmartPtr<int, NoCheckPolicy> nocheckPtr = ptr;
    
    std::cout<<*nocheckPtr<<'\n';
    std::cout<<*ptr<<'\n';
    
    ptr = make_smart(3);
    nocheckPtr = ptr;
    
    std::cout<<*ptr<<'\n';
    
    *ptr = 4;
    
    std::cout<<*ptr<<'\n';
}

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Compilation time: 0.39 sec, absolute service time: 0.58 sec (cached)

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Error(s):

source_file.cpp: In instantiation of ‘SmartPtr<T, CheckingPolicy>::SmartPtr(const SmartPtr<T, ChkPolicy>&) [with ChkPolicy = FullCheckPolicy; T = int; CheckingPolicy = NoCheckPolicy]’:
source_file.cpp:102:47:   required from here
source_file.cpp:33:8: error: ‘int* SmartPtr<int, FullCheckPolicy>::p_’ is private
source_file.cpp:59:9: error: within this context
source_file.cpp: In instantiation of ‘SmartPtr<T, CheckingPolicy>& SmartPtr<T, CheckingPolicy>::operator=(const SmartPtr<T, ChkPolicy>&) [with ChkPolicy = NoCheckPolicy; T = int; CheckingPolicy = FullCheckPolicy; SmartPtr<T, CheckingPolicy> = SmartPtr<int, FullCheckPolicy>]’:
source_file.cpp:107:23:   required from here
source_file.cpp:33:8: error: ‘int* SmartPtr<int, NoCheckPolicy>::p_’ is private
source_file.cpp:66:9: error: within this context
source_file.cpp:67:5: warning: no return statement in function returning non-void [-Wreturn-type]
source_file.cpp: In instantiation of ‘SmartPtr<T, CheckingPolicy>& SmartPtr<T, CheckingPolicy>::operator=(const SmartPtr<T, ChkPolicy>&) [with ChkPolicy = FullCheckPolicy; T = int; CheckingPolicy = NoCheckPolicy; SmartPtr<T, CheckingPolicy> = SmartPtr<int, NoCheckPolicy>]’:
source_file.cpp:108:18:   required from here
source_file.cpp:33:8: error: ‘int* SmartPtr<int, FullCheckPolicy>::p_’ is private
source_file.cpp:66:9: error: within this context
source_file.cpp:67:5: warning: no return statement in function returning non-void [-Wreturn-type]