There has got to be a better way

**cunnus88** · 04-02-2009

It's a solution I came up with to a template specialization problem which is really crappy. And if there are any other, better, cleaner ways to do it, please enlighten me.

I have a templated node class with a lot of member variables and functions. With the exception of ONE member function, everything else is the same. For this one exceptional function, the behavior is different depending on what the template type is. So here's my solution:

Code:

class A;
class B;

template <typename T>
class node {
  void recursive_function(node<A>* nt) {
    do_foo;
    recursive_function(nt);
  }

  void recursive_function(node<B>* nt) {
    do_bar;
    recursive_function(nt);
  }
}

//main body of program
  node<A>* na = new node<A>;
  node<B>* nb = new node<B>;

  na->recursive_function(na);
  nb->recursive_function(nb);

One solution would be to change it into an inheritance relationship, but I'd have to change many other places in my program to conditional statements. So I'd like to avoid doing that.

Is there a better way to do what I'm doing?

**matsp** · 04-03-2009

I'm pretty sure that the RIGHT way to do that would be, as you suggest, to have a base-class with a virtual function that you override in A and/or B to do do_foo and do_bar respectively.

Or at least, let each node have a member function that does either do_foo or do_bar.

--
Mats

**cunnus88** · 04-03-2009

Sorry, I didn't give full details. The template node itself is subsumed under several other classes in different ways. Like

Code:

template<typename T>
class OneClass {
node<T> one_node;
};

template<typename T>
class AnotherClass {
node<T> another_node;
};

And it's actually these things that are being called by the main program. So if I modify "node" in a fundamental way like that, it'll take me a while to untangle all the other dependent modules.

Anyway, thanks. Judging by your comment, I'm guessing there's no clean way of doing this with purely templatic methdods.

**Elysia** · 04-03-2009

Why, I'm pretty sure you can specialize member functions of a template class.

**cunnus88** · 04-03-2009

Could you tell me how? I've looked at several articles on template specialization and it doesn't seem as if specialization of template member functions is possible. I've tried some variations myself and the compiler tells me no dice.

**Elysia** · 04-03-2009

Code:

#include <iostream>

template<typename T> class foo
{
public:
	void foo2();
};

template<typename T> void foo<T>::foo2()
{
	 std::cout << "Hi, I'm foo!\n";
}

template<> void foo<int>::foo2()
{
	std::cout << "Hi, I'm a retarded foo!\n";
}

int main()
{
	foo<double> d;
	foo<int> i;
	d.foo2();
	i.foo2();
}

Output:
Hi, I'm foo!
Hi, I'm a retarded foo!
Press any key to continue . . .

**cunnus88** · 04-03-2009

Oh wow. That worked.

Thanks Elysia. You're a programming master! How the hell do you know every thing?

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