Template Method within Template class definition does not match declaration

Question

I have made a template class LinkedList of template class T and within this class, I want to implement a function enqueue that takes data of a general type D and calls the T con

Answer 1

You need to define your function body as:

template <typename T>
template <typename D>
bool LinkedList<T>::enqueue (D& newData) {
  // ...
}

Also, const D& is probably cleaner. It would be even better to use perfect forwarding, to allow passing any kind of reference type:

template <typename T>
template <typename D>
bool LinkedList<T>::enqueue (D&& newData) {
  // ...
  newNode->_value = new T (std::forward<D>(newData));
}

This can also be made to work with an arbitrary number of parameters to the constructor:

template <typename T>
template <typename... D>
bool LinkedList<T>::enqueue (D&&... newData) {
  // ...
  newNode->_value = new T (std::forward<D>(newData)...);
}

Additionally, your code isn't exception-safe. If the T constructor throws an exception, the newNode instance is never freed, causing a memory leak.

Also, don't use NULL, but use nullptr if possible (i.e. if you can use C++11).