C++ Template Template Parameters 🎯

Welcome to our deep dive into C++ Template Template Parameters! This lesson is designed to help you understand this powerful feature that allows you to create flexible, reusable, and self-parameterizing templates. Let's get started!

What are Template Template Parameters? 📝

In C++, Template Template Parameters (TTP) are an extension of templates that allow you to create templates of templates. This means you can define a template that takes another template as a parameter.

Why might you want to use this? Well, TTPs allow you to create generic algorithms that work with any container, regardless of the container's type.

Syntax 💡

The syntax for Template Template Parameters is as follows:

cpp

template<template<class T> class TemplateType, class OtherType>
class MyTemplate;

Here, TemplateType is the template template parameter, and OtherType is a regular type parameter.

Example 1: A Stack Class for Different Containers 📝

Let's create a simple Stack class that works with any container that supports push_back() and size().

cpp

template<template<class T, size_t N> class Container>
class Stack {
private:
    Container<int> stack;

public:
    void push(int value) {
        stack.push_back(value);
    }

    int pop() {
        if(!stack.empty()) {
            int value = stack.back();
            stack.pop_back();
            return value;
        }
        return -1;
    }

    int size() {
        return stack.size();
    }
};

In this example, Container is a template template parameter, which means it can take any container as a template. Here, we've used a simple container that holds integers, but you could use any container that supports push_back() and size().

Example 2: A Max Heap Using Template Template Parameters 💡

Now, let's create a Max Heap class that works with any container that supports push(), size(), and operator<().

cpp

template<template<class T> class Container, class T>
class MaxHeap {
private:
    Container<T> heap;

public:
    void insert(const T& value) {
        if(heap.empty() || value > heap.front()) {
            heap.push_front(value);
        } else {
            auto it = heap.begin();
            while(it != heap.begin() && value > *it) {
                it = heap.erase(it);
                it = heap.begin();
            }
            heap.insert(value);
        }
    }

    T extractMax() {
        if(heap.empty()) return -1;
        return heap.erase(heap.begin());
    }

    bool empty() {
        return heap.empty();
    }
};

In this example, we've created a MaxHeap that can work with any container that supports push(), size(), and operator<().

Quiz 📝

By now, you should have a good understanding of Template Template Parameters in C++. Happy coding! 💻 🚀