Module 05 Solutions

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Exercise 00: Bureaucrat

Nested exception classes.

Bureaucrat.hpp

class Bureaucrat {
private:
    const std::string _name;
    int _grade;  // 1 (highest) to 150 (lowest)

public:
    class GradeTooHighException : public std::exception {
    public:
        const char* what() const throw() {
            return "Grade is too high!";
        }
    };

    class GradeTooLowException : public std::exception {
    public:
        const char* what() const throw() {
            return "Grade is too low!";
        }
    };

    Bureaucrat(const std::string& name, int grade);
    // ... OCF ...

    void incrementGrade();  // Throws if would go below 1
    void decrementGrade();  // Throws if would go above 150
};

Bureaucrat.cpp

Bureaucrat::Bureaucrat(const std::string& name, int grade)
    : _name(name), _grade(grade)
{
    if (grade < 1)
        throw GradeTooHighException();
    if (grade > 150)
        throw GradeTooLowException();
}

void Bureaucrat::incrementGrade() {
    if (_grade - 1 < 1)
        throw GradeTooHighException();
    _grade--;
}

---

Exercise 02: Abstract Form

Concrete form classes inherit from AForm.

AForm.hpp

class AForm {
protected:
    const std::string _name;
    bool _signed;
    const int _gradeToSign;
    const int _gradeToExecute;

public:
    virtual void execute(Bureaucrat const& executor) const = 0;

    class FormNotSignedException : public std::exception {
        const char* what() const throw() { return "Form not signed!"; }
    };
};

ShrubberyCreationForm.cpp

void ShrubberyCreationForm::execute(Bureaucrat const& executor) const {
    if (!_signed)
        throw FormNotSignedException();
    if (executor.getGrade() > _gradeToExecute)
        throw GradeTooLowException();

    std::ofstream file((_target + "_shrubbery").c_str());
    file << "       _-_" << std::endl;
    file << "    /~~   ~~\\" << std::endl;
    // ... ASCII tree ...
    file.close();
}

---

Exercise 03: Intern Factory

Function pointers to avoid if/else chains.

Intern.cpp

typedef AForm* (*FormCreator)(const std::string&);

static AForm* createShrubbery(const std::string& target) {
    return new ShrubberyCreationForm(target);
}

static AForm* createRobotomy(const std::string& target) {
    return new RobotomyRequestForm(target);
}

static AForm* createPresidential(const std::string& target) {
    return new PresidentialPardonForm(target);
}

AForm* Intern::makeForm(const std::string& name, const std::string& target) {
    std::string names[] = {
        "shrubbery creation",
        "robotomy request",
        "presidential pardon"
    };
    FormCreator creators[] = {
        createShrubbery,
        createRobotomy,
        createPresidential
    };

    for (int i = 0; i < 3; i++) {
        if (name == names[i]) {
            std::cout << "Intern creates " << name << std::endl;
            return creators[i](target);
        }
    }
    std::cerr << "Form not found: " << name << std::endl;
    return NULL;
}