OOP model

Set up the class hierarchy and templates.

Template function: printItem

In this lesson we add a template function named printItem. This function can print any type with std::cout.

Example: template <typename T> void printItem(const T& item) { std::cout << item; }. This function can be called for a std::string, a bool or a Task object. Templates let the same code work for different types. The const T& parameter prevents copying and is efficient for large objects. We take the Task class from the previous lesson and add this template on top.

Calling the template

When calling a template function you do not specify the type explicitly; the compiler deduces it from the parameter. The call printItem(t.title) sets T to std::string.

Example: printItem(t.title); prints the title, printItem(t.done); prints the done flag. The compiler generates the correct type for each call. This is not shorter than writing std::cout << but provides consistency when used repeatedly in a project. Templates are also common in the STL; std::vector is a template too.

Exercise Add the printItem template and call it

After the Task class in the starting code, add the printItem template function: template <typename T> void printItem(const T& item) { std::cout << item; }. In main print the title with printItem(t.title), then a space and t.done.

Show example solution

#include <iostream>
#include <string>

class Task {
public:
    std::string title;
    bool done;
    Task(std::string t) : title(t), done(false) {}
};

template <typename T>
void printItem(const T& item) {
    std::cout << item;
}

int main() {
    Task t("Homework");
    printItem(t.title);
    std::cout << " " << t.done;
    return 0;
}

Test yourself

Complete the template definition

template <____> void printItem(const T& item) { std::cout << item; }

Show answer

template <typename T> void printItem(const T& item) { std::cout << item; }

What does template <typename T> enable?
```
template <typename T>
void printItem(const T& item);
```
- The function is deleted
- The function is faster
- The function is hidden
- The function works with different types
Show answer

The function works with different types — A template lets the function work with different types.
Match each piece to its role

template <typename T>

Template definition
const T&

Copy-free parameter
printItem(t.title)

Call
std::cout << item

Printing

Next lesson: STL layer

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