Tutorial 9: Generic Programming, Webots III

Generic Programming

1. What is generic programming?

2. Refactor this program so that it uses template functions.

#include <iostream>
#include <vector>

void print(int val) { std::cout << val << std::endl; }
void print(double val) { std::cout << val << std::endl; }
void print(std::string val) { std::cout << val << std::endl; }
void print(std::vector<int> val) {
    for (auto const& e : val)
        std::cout << e << ", ";
    std::cout << std::endl;
}

int main() {
    print(2);
    print(4.2);
    print("hello");
    print(std::vector<int>{1, 2, 3});
}

3. Why can’t this code compile?

// print.hpp
#pragma once
template <typename T>
void print(T val);

// print.cpp
#include <iostream>
#include "print.hpp"
template <typename T>
void print(T val) { std::cout << val; }

// main.cpp
#include "print.hpp"
int main() {
    print("Hello World!");
}

4. Write a class called Union which accepts two datatype parameters <U, V> and switches types based on the currently set type. It should have the following methods:

• Constructor for value of type U
• Constructor for value of type V
• Setters which will set the new value of type either U or V.
• isType<T> which checks if currently set type is of type T
• operator<< overload to print the union value

The following program shows how the union should be used and its expected values.

int main() {
    std::cout << std::boolalpha; // Print true/false instead of 1/0.

    Union<double, std::string> obj(3.3);
    std::cout << obj << "\n";                       // 3.3
    std::cout << obj.isType<double>() << "\n";      // true
    std::cout << obj.isType<std::string>() << "\n"; // false

    obj.set("Now a string");
    std::cout << obj << "\n";                       // "Now a string"
    std::cout << obj.isType<double>() << "\n";      // false
    std::cout << obj.isType<std::string>() << "\n"; // true
}

Webots III

The starter code for this tutorial can be found here.

5. Open the Webots controller “Pose”. This controller should constantly output its pose which is a tuple with 4 elements (X, Y, Z, R) where:

• XYZ are the 3D position of the robot in metres.
• R is the global heading of the robot about the Z axis in radians.

A sample output of a pose is as follows:

X: -14.75    Y:  10.11    Z:   0.00    R:   3.14

Verify the output is correct by dragging the robot around with the mouse.

a. Use the GPS device to read in the robot’s pose.

b. Use the compass device to read in the robot’s absolute heading with the positive y-axis as global north. It is important to consider that the compass device returns a 3D-vector of “northness” along their respective XYZ axes. Therefore the angle between two values is needed.

6. Open the Webots controller “ClosestObject”. Use the lidar device so that this controller gets the distance and (x, y) position of the closest object to the robot.