[RESOLVED] Passing a function pointer as template argument to a class

[treuss]

Hi all,

I have in the past written code for templated functions where one function argument can be either a function pointer or a Functor. Works pretty straightforward.

Now I am in a situation where I am actually trying to pass a function pointer as template argument to a class. Unfortunately this does not work, I can pass the Functor class but not the function pointer. Below code illustrates the issue:

#include <string>
#include <iostream>
#include <sstream>

#include <cstdlib>

// For demonstration
const char * external_library_call() {
	return "FFFF";
}

// Default conversion from const char * to native type. This shall be specialized!
template<typename T>
class StandardConverter
{
public:
	T operator()(const char * str) {
		std::istringstream is(str);
		T t;
		is >> t;
		return t;
	}
};

// Special conversion function. There might be many of these.
std::string hex2dec(const char * str) {
	std::ostringstream os;
	os << strtol(str, 0, 16);
	return os.str();
}

// Field class
template<typename T, typename F = StandardConverter<T> >
class Field
{
private:
	F f;
public:
	T get()
	{
		return f(external_library_call());
	}
};

// Record class
class Record
{
public:
	Field<std::string> I_FIELD1;
	Field<std::string, StandardConverter<std::string> > I_FIELD2;
	// Field<std::string, hex2dec> I_FIELD3;
};

int main()
{
	Record rec;
	std::cout << rec.I_FIELD1.get() << std::endl;
	std::cout << rec.I_FIELD2.get() << std::endl;
	// std::cout << rec.I_FIELD3.get() << std::endl;
}

The idea is to have the definition of the Record class simple and readable and have a maintainable way to add auto-conversion functions to the class. So the lines I commented out are the desirable way how I want my code to look. Unfortunately I could not come up with any way that was close to readable for solving this.

Does anybody have any good suggestions?