Homework 5 Details for MPCS 51410

Each homework assignment will consist of a small problem in some OO code, which is somehow problematic, given your developing understanding of good OO best practices and patterns, you will improve, thus eliminating any negative issues in the code you are given. Each homework assignment is intended to give every student hands-on experience with the core concepts covered during the course.  You may code your solution to the problem in any legitimate OO language of your choice.  You need to submit labs to the TAs for grading--see submission instructions below.  Generally, unless otherwise specified, you will have one week to complete each assigned homework problem.

See the syllabus for information on grading.  Turning in lab assignments on time is required, without exception, and all late deliveries will be penalized, regardless of cause.  Submit your assignments to the subversion repository according to the directions on the syllabus page.

You may write these solutions in any programming language of your choice.  Our suggestion is now is not the time to learn a new programming language along with the concepts themselves.  So our suggestion is to use whatever programming language you  know best.

Homework 5   Due: 5:00 pm, Monday, March 8, 2021

Coding Problem: 

BACKGROUND:

Like all programming-related problems, learning a new programming language or style is not an exercise in reading but rather an exercise in thinking and typing.  This homework is designed to give you  hands-on experience in some fundamental skills involved in object-oriented design and coding.  You will generally find the References section below helpful in addition to the required and recommended reading. 

WHAT YOU NEED TO DO:

 Download the code here.  You are to read and understand the code, what it is intending to accomplish, and what the responsibilities are of the class or classes.  Nonetheless, there are one or more problems in the code which require your insight in their amelioration.  Your mission, should you choose to accept it, is to "fix" the problem(s) in the code, without introducing any new problems, by coding a replacement set of code in any legitimate object-oriented programming language of your choice.  Be sure to include a README with instructions on how to compile (if necessary) and run your coded solution.

Very important:  Inside comments at the top of your coded solution, you are to fully describe the problem(s) in the original code as you have determined it, and describe why your solution eliminates the original problem(s).

Step 1:

Change into the Step.1 subdirectory.  Take a look at the C++ files there.  Don't worry, if you don't know C++, we've provided a Makefile that you can run to build the program called "mfp_printer."  All you have to do to build the program is type "make" and hit return.  [NOTE:  If you encounter errors, it means you have not set up g++ to run.  If you're running a linux laptop, you should never see this error.  If you are running a Mac laptop, it means you will need to install Apple's XCode software (or just run it on the cluster...see below).  You should go here and follow the instructions for installing the XCode command line tools.  If you are running Windoze, you can avoid all this effort if you just scp the downloaded gz file to the cluster.  It will all run just fine there.  In fact, anyone, even Mac people, can run this on the cluster to simplify their lives.]

Examine the code in the Step.1 subdirectory.  Make sure you understand the call path starting with the main() function (in Main.cpp).  It's a very simple program and should not take you long to figure out what's going on.  You may type make and it will compile the code and you can execute it by running the generated output, mfp_printer.

Step 2:

After you have an idea of what's happening with the Step.1 code (pay particular attention to the instantiation of a new Cartridge in Printer.cpp), change to the Step.2 directory, and type make.  You will see some errors.  To wit (at least on the Mac):

~/UofC/51410/src/D/Step.2:$ make
g++ -I. -g -Wall -ansi -c Printer.cpp
Printer.cpp:8:25: error: no matching constructor for initialization of 'Cartridge'
    Cartridge * c = new Cartridge( name );
                        ^          ~~~~
./Cartridge.h:9:7: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from
      'std::__1::string' (aka 'basic_string<char, char_traits<char>, allocator<char> >') to 'const Cartridge' for 1st
      argument
class Cartridge
      ^
./Cartridge.h:12:3: note: candidate constructor not viable: requires 2 arguments, but 1 was provided
         Cartridge(string model_no, int num_pages);
         ^
1 error generated.
make: *** [Printer.o] Error 1
[mark@MusicServer]~/UofC/51410/src/D/Step.2
$

Running the same make command on linux gives a similar set of errors:

mark@poster:/tmp/Step.2$ make
g++ -I. -g -Wall -ansi -c Main.cpp
g++ -I. -g -Wall -ansi -c Printer.cpp
Printer.cpp: In member function ‘void Printer::prepare()’:
Printer.cpp:8:41: error: no matching function for call to ‘Cartridge::Cartridge(std::__cxx11::string&)’
     Cartridge * c = new Cartridge( name );
                                         ^
In file included from Printer.cpp:2:0:
Cartridge.h:12:3: note: candidate: Cartridge::Cartridge(std::__cxx11::string, int)
   Cartridge(string model_no, int num_pages);
   ^
Cartridge.h:12:3: note:   candidate expects 2 arguments, 1 provided
Cartridge.h:9:7: note: candidate: Cartridge::Cartridge(const Cartridge&)
 class Cartridge
       ^
Cartridge.h:9:7: note:   no known conversion for argument 1 from ‘std::__cxx11::string {aka std::__cxx11::basic_string<char>}’ to ‘const Cartridge&’
Makefile:21: recipe for target 'Printer.o' failed
make: *** [Printer.o] Error 1

You should notice that the program will not build, and it will not build because in the Step.2 code, the constructor for a Cartridge has changed, and that change has affected the code in Printer.cpp, specifically on line 7 or 8:

Cartridge * c = new Cartridge( name );

The key takeaway here is that the Printer.cpp file is dependent on the concrete class Cartridge, and specifically, it's constructor.  In light of our SOLID principles, as well as our creational patterns, please take the Step.2 code, rewrite it in any OO language you'd like (including C++), and fix the problem(s).  For hints, see the References section below.

References:

You may find the following references helpful:

https://web.archive.org/web/20110714224327/http://www.objectmentor.com/resources/articles/dip.pdf

https://en.wikipedia.org/wiki/Dependency_inversion_principle

https://www.martinfowler.com/articles/dipInTheWild.html

Submitting:

Use the folder named "hw5" in your Subversion repository. See the syllabus for more info about submission using Subversion. Upload your HW5 solution file(s) and any supporting materials to the repo.