template enable if is pointer

Question

I try to make a class to manage resources easily (ResourceManager).

For that I use the template with C++11.

Here's what I do:

---

template<class K,class T>
class ResourceManager
{
    public:
        ResourceManager();
        ~ResourceManager();

        /* code */

        void clear();

    private : 
        std::unordered_map<K,T> resource;

        template <bool b>
        void clear();
};

---

 template<class K,class T>
 void ResourceManager<K,T>::clear()
 {
    clear<std::is_pointer<T>::value>();
 };

 template<class K,class T>
 template<bool b>
 void ResourceManager<K,T>::clear<b>()
 {
    for(auto& x:resource)
    delete x.second;
    resource.clear();
 }

 template<class K,class T>
 template<>
 void ResourceManager<K,T>::clear<false>()
 {
    resource.clear();
 }

---

In short, I try to have different comportement if T is a pointer (auto delete).

I tried to use std::enable_if, but I did not understand how it functioned, and if this is the right way to take.

If someone could help me...

---

Code can be found here: https://github.com/Krozark/ResourceManager

Answer 1

You could just use a solution based on overload and tag dispatching. Your clear() member function would be defined this way:

void clear()
{
    do_clear(std::is_pointer<T>());
}

And your class template would include two overloads of do_clear(), as follows:

template<class K,class T>
class ResourceManager
{

    // ...

private:

    void do_clear(std::true_type);
    void do_clear(std::false_type);

};

And here is the definition of those two member functions:

template<class K, class T>
void ResourceManager<K, T>::do_clear(std::true_type)
{
    for(auto& x:resource)
    delete x.second;
    resource.clear();
}

template<class K, class T>
void ResourceManager<K, T>::do_clear(std::false_type)
{
    resource.clear();
}

Notice, however, that you always have the option of using smart pointers and other RAII resource wrappers to avoid calling delete explicitly on raw pointers.