如何使用模板化的 class 作为参数类型？

Question

I am new to C++ and I know this is very basic, but I couldn't determine the correct keywords to find a solution to this particular problem I'm having.

So say I have two classes: Food and Dog. Food is a template class. I then want to pass a food object as an argument into a function called "eat" in Dog. What is the best way of doing this? Here is what I assumed would make the most sense, but it doesn't work.

// main.cpp
#include <iostream>
#include "food.h"
#include "food.cpp"
#include "dog.h"

int main(void)
{
    Food<int> *food = new Food(10);
    Dog *dog = new Dog();
    dog->eat(food);
    
    delete food;
    delete dog;
    
    return 0;
}

// dog.h
#pragma once

class Dog()
{
public:
    Dog();
    ~Dog();
    void eat(Food<T>);
};

// dog.cpp
#include "dog.h"

Dog() {}

~Dog() {}

void eat(Food<T> food)
{
    std::cout << "Eating food\n";
}

// food.h
#pragma once

template <class T>
class Food
{
public:
    Food(T value);
    ~Food();
    
    T value = -1;
};

// food.cpp
#include "food.h"

template <class T>
Food<T>::Food(T value): value(value) {}

template <class T>
Food<T>::~Food() {}

Does Dog also need to be made a template class just to pass in a template object to a single fucntion? That seems like a very convoluted way of doing it if there are 20 functions in a class, only one of which takes an argument that is templated, so I thought there might be a better alternative.

Answer 1

You don't need to make the whole class dog template, you might just have template method:

template <class T>
class Food
{
public:
    Food(T value) : value(value) {}

    T value;
};

class Dog
{
public:

    template <typename T>
    void eat(Food<T>) { std::cout << "Eating food\n"; }
};

int main()
{
    Food<int> food(10);
    Dog dog;
    dog.eat(food);
}