CODEWITHSUNDEEP
c++templates
user245019
user245019

Reputation:

Returning templates

Is it possible to return a template?

This is what I've been trying, but this isn't working.

template<int degree>
class Polynomial
{
public:

   ... ususal stuff ...

   // Polynimal<degree - 1>
   Polynomial derivative() { /* returns a different template */ }

};


int main()
{
   Polynomial<3> cubic;
   Polynomial<2> parabola;

   parabola = cubic.derivative();
}

Is this possible? What little nugget am I missing?

Upvotes: 2

Views: 129

Answers (3)

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361482

degree is known at compile time, so you can use degree -1 as value argument in the return type:

template<int degree>
class Polynomial
{
public:

   Polynomial<degree-1> derivative() 
   {  
         Polynomial<degree-1> d;
         //...
         return d;
   }
};
int main() {
         Polynomial<3> cubic;
         Polynomial<2> parabola;
         parabola = cubic.derivative();
        return 0;
}

Demo : http://www.ideone.com/44Pc7

Upvotes: 4

BЈовић
BЈовић

Reputation: 64223

I assume that you want this :

template<int degree>
class Polynomial
{
public:

   ... ususal stuff ...

   // Polynimal<degree - 1>
   Polynomial< degree-1 > derivative() {
     Polynomial< degree-1 > res;
     //assign values
     return res
   }

};

Make sure that in you specialization for Polynomial<0> the method derivative doesn't exits.

Upvotes: 3

Bj&#246;rn Pollex
Bj&#246;rn Pollex

Reputation: 76828

You can make the member-function a function template:

template<int ret_degree>
Polynomial<ret_degree> derivative() { /* returns a different template */ }

Or, if you know the degree of the return-polynomial, you can do something like this:

Polynomial<degree-1> derivative() { /* returns a different template */ }

Upvotes: 6

Related Questions