Testing C++ Template Inheritance

TestTemplateInheritance.cpp

#define _WIN32_WINNT 0x0601

#ifdef _MSC_VER
#include <boost/config/compiler/visualc.hpp>
#endif

#include <cstdlib>
#include <string>
#include <sstream>
#include <iostream>
#include <boost/asio.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/concepts.hpp> 
#include <boost/make_shared.hpp>
#include <boost/exception/all.hpp>

using namespace boost;

class socket_stream_source : public iostreams::source
{
	int max=100;
public:
	socket_stream_source(int max)
	{
		this->max = max;
	}


	std::streamsize read(char* s, std::streamsize n)
	{
		printf("n: %lld\n", n);

		if (!max)
			return -1;

		for (int i = 0; i < n; i++) {
			if (!max--)
				return i;
			s[i] = 0;
		}
		return n;
	};
};

int main_this_fails()
{
	// this fails completely because templated classes not be upcast even if the type parameters are inherited
	boost::iostreams::stream<boost::iostreams::source> *sock_stream2 =
		static_cast <boost::iostreams::stream<boost::iostreams::source>*>(
			new boost::iostreams::stream<socket_stream_source>()
			);

	// try with reinterpret_cast, this fails because boost::iostreams::source does not contain a read function
	boost::iostreams::stream<boost::iostreams::source> *sock_stream2 =
		reinterpret_cast <boost::iostreams::stream<boost::iostreams::source>*>(
			new boost::iostreams::stream<socket_stream_source>()
			);

	// try with c style cast, this fails because boost::iostreams::source does not contain a read function
	boost::iostreams::stream<boost::iostreams::source> *sock_stream3 =
		(boost::iostreams::stream<boost::iostreams::source>*)
		new boost::iostreams::stream<socket_stream_source>();

	
	return 0;
}