Question

I have a bunch of overloaded functions that operate on certain data types such as int, double and strings. Most of these functions perform the same action, where only a specific set of data types are allowed. That means I cannot create a simple generic template function as I lose type safety (and potentially incurring a run-time problem for validation within the function).

Is it possible to create a “semi-generic compile time type safe function”? If so, how? If not, is this something that will come up in C++0x?

An (non-valid) idea;

template <typename T, restrict: int, std::string >
void foo(T bar);
...
foo((int)0); // OK
foo((std::string)"foobar"); // OK
foo((double)0.0); // Compile Error

Note: I realize I could create a class that has overloaded constructors and assignment operators and pass a variable of that class instead to the function.

Answer 1

Use sfinae

template<typename> struct restrict { };
template<> struct restrict<string> { typedef void type; };
template<> struct restrict<int> { typedef void type; };

template <typename T>
typename restrict<T>::type foo(T bar);

That foo will only be able to accept string or int for T. No hard compile time error occurs if you call foo(0.f), but rather if there is another function that accepts the argument, that one is taken instead.