How to reuse function specialization code? - c++

Question

#include <iostream>
using namespace std;
template<typename T>
void fun(const T & val)
{
cout << " T " << endl;
}
template<>
void fun<int>(const int & val)
{
cout << " specialization same code " << val << endl;
}
template<>
void fun<double>(const double& val)
{
cout << " specialization same code " << val << endl;
}
int main()
{
fun( 1 );
fun( 1.0 );
fun( 'c' );
return 0;
}
Question> Is there a way that I can reuse the function specialization code?
For example, assume both 'int and 'double' specialization has the exactly same implementation code. Is there a method I can prevent the code duplication?
http://codepad.org/awGYWiWv
Thank you

Answer 1

As suggested by #0x499602D2 in the comments, create another function and make sure it gets called only for int or double.
template<typename T>
void bar(const T & val)
{
// Make sure this gets called only for int or double.
static_assert(std::is_same<T, int>::value || std::is_same<T, double>::value);
// Do useful stuff with val.
}
template<>
void fun<int>(const int & val)
{
bar(val);
}
template<>
void fun<double>(const double& val)
{
bar(val);
}

Answer 2

To reuse the same code for multiple types of the same kind, you could use std::enable_if (or boost::enable_if if you are not using C++11) with type traits (a nice example is here).
e.g.:
template<typename T>
typename std::enable_if<std::is_floating_point<T>::value, T>::type
fun(const T& val)
{
cout << " floating point specialisation " << val << endl;
}
(function specialisations of this kind work only in C++11, but you can use a struct or class for the same purpose in older C++ versions)

Answer 3

something like this should give you the level of re-use you want:
#include <iostream>
#include <type_traits>
using namespace std;
// will only compile if T is an arithmetic type
template<typename T,
typename std::enable_if<
std::is_arithmetic<T>::value>::type* = nullptr>
void fun(T val)
{
cout << "the square is " << val * val << endl;
}
int main()
{
int x = 10;
double y = 10;
fun(x);
fun(y);
return 0;
}