C++ Type Specifier

varspec.cpp

#include <typeinfo>
#include <functional>
#include <iostream>
#include <map>

struct TypeSpec
{
	const char * name; // pure name
	std::function<bool(std::ostream&,void*)> out; // conversion fx
	const std::type_info & ti; // internal name (unique)

	TypeSpec(const char * xname,const std::type_info & xti, std::function<bool(std::ostream&,void*)>  xout);
};

std::map<std::string,TypeSpec *> types; // registry

TypeSpec::TypeSpec(const char * xname, const std::type_info & xti, std::function<bool(std::ostream&,void*)>  xout):
	name(xname),out(xout),ti(xti)
{
	types[ti.name()] = this;
}

/// lookup at compile time
template <class T>
TypeSpec * findtype()
{
	auto it = types.find(typeid(T).name());
	if(it != types.end())
		return it->second;
	else
		return 0;
}

/// registration
#define TYPESPEC(T) \
	TypeSpec T##_spec = TypeSpec ( #T, typeid(T), \
		[] (std::ostream & ons, void * p) -> bool { \
			ons << *(T*)p;\
			return (bool)ons;\
		}  \
	);


TYPESPEC(int);
TYPESPEC(float);

int main(int argc, char * argv[])
{
	for(auto & t : types)
	{
		std::cout << t.first << " " << t.second->name << std::endl;
	}	
	int w = 10;
	findtype<int>()->out(std::cout,&w);
}