Thread: Templated Classes with Templated Functions

Based on reading here:

Cprogramming.com - Tutorials - Templated Functions

I understand that such thing is possible, however I have the following code:

Code:

template <int X, int Y>
class Simulator
{
public:
  template<int N, int N1>
  void doom::vector<State, N>& run(doom::vector<Input, N1>& input, double ts);
protected:
  //some variables here
}


//here's my implementation
template <int X, int Y>
template<int N, int N1>
const doom::vector<State, N>& Simulator<X,Y>::run(doom::vector<Input, N1>& input, double ts);
{
 //some code here
 return x;
} 


//here's my test
int main(){
Simulator<25, 25> s( new Vehicle( WB ) );
doom::vector<Input, 25> u = InputLibrary::getSimpleInputSet( );
//this is where the error happened
doom::vector<State, 25> x = s.run( u, 0.1 );
}

my error is the following:
error: no matching function for call to âSimulator<25, 25>::run(ece373::vector<ece373::vector<double, 2>, 25>&, double)â

You need to specify the template parameters to run() explicitly because N is not determinable from the parameters.

Code:

s.run<25,25>( u, 0.1 );

Code:

template <int X, int Y>
Simulator<X, Y>& 
Simulator<X,Y>::operator=( const Simulator& other )

I suppose the template arguments are not strictly necessary for the argument (e.g once it becomes clear it is a member function, Simulator will be implicitly treated as Simulator<X, Y>, but you may add it there as well.

You need to define those functions.

Originally Posted by -EquinoX-

can someone tell me what's wrong with this:

Code:

template <int X, int Y>
Simulator& 
Simulator<X,Y>::operator=( const Simulator& other )
{
	if( &other != this )
	{
		delete v;
		v = new Vehicle();
		*v = *other.v;
		x = other.x;
		u = other.u;
	}
	
	return *this;
}

Again here is code that checks for self-assignment, which is a bad thing to need to check for. I shall reiterate again that this code is not exception safe because the new statement might throw an exception, but v is already deleted. Then when the Simulator is destructed it would attempt to delete "v" a second time, leading to a fatal program termination. Read these two articles for a full explanation.
GotW #11: Object Identity
GotW #23: Object Lifetimes - Part II

Not only that, but the actual code of the assignment operator really leaves one thinking that there is no point in v being a pointer rather than just a member. Afterall, this assignment operator already assumes that the pointer is not NULL, is dynamically allocated, and has an assignment operator of its own.
I would suggest making "v" an object rather than a pointer and deleting this assignment operator entirely as everything in the class is then already capable of assignment through the compiler generated version.
The only reason not to would be if Vehicle doesn't have a non-throwing swap method but Simulator does.