PIMPL Idiom in C++

PIMPL Idiom Example

// PIMPL Idiom
// Example by Patrick Hebron

#include <memory>
#include <string>
#include <iostream>

/** @brief templated pimpl wrapper */
template <typename Impl> class pimpl_t {
public:
	
	typedef std::shared_ptr<pimpl_t> ref; //!< shared_ptr type for pimpl wrapper
	
private:
	
	std::unique_ptr<Impl> m_impl; //!< the implementation object
	
	/** @brief explicit argument-forwarding constructor */
	template <typename ... Args> explicit pimpl_t(Args&& ... args)
	: m_impl( std::unique_ptr<Impl>( new Impl( std::forward<Args>( args )... ) ) ) { /* no-op */ }
	
public:
	
	/** @brief destructor */
	~pimpl_t() { /* no-op */ }
	
	/** @brief static creational method */
	template <typename ... Args> static pimpl_t::ref create(Args&& ... args)
	{
		return pimpl_t::ref( new pimpl_t( std::forward<Args>( args )... ) );
	}
	
	/** @brief argument-forwarding construction setter */
	template <typename ... Args> void set_ptr(Args&& ... args)
	{
		m_impl = std::unique_ptr<Impl>( new Impl( std::forward<Args>( args )... ) );
	}
	
	/** @brief returns const pointer to implementation */
	const Impl* get_ptr() const
	{
		return m_impl.get();
	}
	
	/** @brief returns pointer to implementation */
	Impl* get_ptr()
	{
		return m_impl.get();
	}
	
	/** @brief returns const reference to implementation */
	const Impl& get_ref() const
	{
		return *( m_impl.get() );
	}
	
	/** @brief returns reference to implementation */
	Impl& get_ref()
	{
		return *( m_impl.get() );
	}
};

struct TestType
{
	std::string m_name;
	int m_id;
	
	TestType(const std::string& i_name, const int& i_id)
	: m_name( i_name ), m_id( i_id ) { /* no-op */ }
};

static inline void print_item(const std::string& label, const pimpl_t<TestType>::ref& item)
{
	std::cout
	<< label << "( " << &item << ", " << item->get_ptr() << " )"
	<< " = { " << item->get_ptr()->m_name << ", " << item->get_ptr()->m_id << " }" << std::endl;
}

int main(int argc, const char * argv[])
{
	pimpl_t<TestType>::ref a;
	pimpl_t<TestType>::ref b;
	
	a = pimpl_t<TestType>::create( "foo", 1234 );
	b = a;
	
	print_item( "a", a );
	print_item( "b", b );
	std::cout << std::endl;
	
	a->set_ptr( "bar", 2345 );
	
	print_item( "a", a );
	print_item( "b", b );
	std::cout << std::endl;

	b->set_ptr( "baz", 3456 );
	
	print_item( "a", a );
	print_item( "b", b );
	std::cout << std::endl;
	
	a->get_ptr()->m_name = "qux";
	
	print_item( "a", a );
	print_item( "b", b );
	std::cout << std::endl;
	
    return 0;
}