Problems recycling c++ lib with templated class for Arduino

Question

I have a header & cpp file located in Arduino\libraries\Parentfolder\Header&Cpp. Arduino IDE recognizes my lib (the class is color coded & Sketch->include library->MyLibrary shows in the dropdown menu and #includes properly).

Problem: Arduino IDE gives undefined reference to MyClass . . . error in my sketch for every reference of the class including function calls. The function fully in other IDEs as header/cpps so I don't think pasting the cody is necessary -- what could I be missing? I've read a million Stack Exchange posts with similar error/watched a million YouTube guides on writing Arduino libs and I can't seem to find the differentiating factors that would make my code not work for Arduino IDE.

tl;dr what are the reasons that a working c++ library (self-made) would not work with Arduino IDE?

/e

Queue.h
#ifndef Queue_h
#define Queue_h
#include "Arduino.h"
template <typename T>
class Queue
{
 public:
 typedef struct node
 {
 T data;
 node * next = nullptr;
 } * nodePtr;
 nodePtr head; // = nullptr;
 nodePtr tail; // = nullptr;
 nodePtr curr; // = nullptr;
 nodePtr temp; // = nullptr;
 unsigned int counter;
 Queue();
 void push(T);
 T& peek();
 T pop();
 int size();
 bool isEmpty();
 void clear();
};
#endif

Queue.cpp

#include "Arduino.h"
#include "Queue.h"
template <typename T>
Queue<T>::Queue()
{
 nodePtr head = nullptr;
 nodePtr tail = nullptr;
 nodePtr curr = nullptr;
 nodePtr temp = nullptr;
 counter = 0;
}
template <typename T>
void Queue<T>::push(T data)
{
 if (head == nullptr)
 {
 head = new node;
 head->data = data;
 tail = head;
 }
 else
 {
 temp = head;
 head = new node;
 head->data = data;
 head->next = temp; 
 }
 counter ++;
}
template <typename T>
T& Queue<T>::peek()
{
 if (head == nullptr)
 {
 return 0;
 }
 return head->data;
}
template <typename T>
T Queue<T>::pop()
{
 // Empty
 if (head == nullptr)
 {
 return 0;
 }
 // Head = tail
 if (head == tail)
 {
 T data = head->data;
 delete head;
 return data;
 }
 // Size > 1
 curr = head;
 while (curr->next != tail)
 {
 curr = curr->next;
 }
 T data = curr->next->data; 
 tail = curr;
 curr = curr->next;
 delete curr;
 counter --;
 return data;
}
template <typename T>
int Queue<T>::size()
{
 return counter;
}
template <typename T>
bool Queue<T>::isEmpty()
{
 if (counter ==0)
 {
 return true;
 }
 return false;
}
template <typename T>
void Queue<T>::clear()
{
 while (head->data != nullptr)
 {
 temp = head->next;
 delete head;
 head = temp; 
 }
 if (head == nullptr)
 {
 return;
 }
 delete head;
 return;
}

.ino

. . .
Queue<float> avgQueue;
. . .

error

. . . In function `__static_initialization_and_destruction_0':
. . . undefined reference to `Queue<float>::Queue()'

SOLVED:

Combining the .cpp contents in the .h and removing the .cpp worked.

• Nick Gammon: Please post a Minimal, Complete, and Verifiable example. Do you have a single sketch file, or have you broken your code into multiple files (eg. cpp/h files)?
• seiqooq: The header and cpp are in the forementioned subfolder which is inside of the Arduino library folder. The errors come from a simple sketch meant only to test the (already-working-in-other-IDEs) library.
• jsotola: one thing that jumps out is the ampersand & in the path ... maybe the compiler does not like it
• seiqooq: That's not the real path, that's just me saying that both the header&cpp are there.

Answer 1

SOLVED:

Putting the .cpp contents in the .h and removing the .cpp from the lib folder entirely worked.

• KIIV: Yes, tempates are instantiated on demand so you have to have complete class inside of header. However I wonder how the pop works if you have the last element. Your head wasn't set to the nullptr - and delete can't do that for you.
• Nick Gammon: Your code doesn't totally prove the problem, however libraries are not included unless you include them in the .ino file which might be your underlying issue.
• Nick Gammon: This, for example, is not complete code: . . . Queue<float> avgQueue; . . .
• seiqooq: @NickGammon fortunately I'm not that much of a noob! The lib was included and everything is now functioning well as a result of the above workaround
• Nick Gammon: I'm glad it is working, however I'm not sure what you did exactly (that didn't work) and what you did (that did work). However this looks relevant.