lab05 : Visitor Design Patern - Part 1

Goals

This is a two part lab. This first half is meant to be a a very simple first pass at looking at the visitor pattern. The purpose is to practice the pattern and associated techology (and the next lab will explore the concepts in more detail with larger code revisions). Learning objectives. At the end of this lab, students should be able to:

• Implement the visitor design pattern for the exisiting code to support a simple visitors pattern to create a combined report for data

Modality

This is a pair lab. You may choose to work alone or with another student. When working in a pair, please always follow good pair programming methodologies. For example, see: https://gds.blog.gov.uk/2018/02/06/how-to-pair-program-effectively-in-6-steps/. In general, set aside time to work togther and share your screen to share the work and learning.

You will need to identify you partner (pair) in your submission (add a header to your main with both your names!). The remaining labs will also be optional pair labs and you will be asked to only partner with the same person twice.

Orientation

At this point, we have a fairly complex program to read in regional data (demographic and hospital) and aggreagate that data to various levels (county and state).
For this week, we will introduce minor changes as an introduction to the visitor pattern. This first pass is intended a very simple addition with minimal changes to our code (and the next lab will explore the concepts in more detail with larger code revisions).

With OO programming, there are some design patterns that can be used ‘to solve recurring design problems to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse’ (https://en.wikipedia.org/wiki/Design_Patterns). This is a rich topic which is difficult to explore in a short time. To get a taste for the design patterns we will explore integrating the visitor design pattern into our exisiting code. This first pass will be very simple (and not take full advantage of this pattern), and we will do further revisions next week.

For this week, the goal is to make minor modifications to use the visitor pattern to print a report combining demographic and hospital data for specified data. You could accomplish this without the visitor pattern, but our goal is to practice this pattern.

Steps

Introduce and modify the following classes as follows to support printing a combined report, using the visitors pattern. 1) Create a visitor class to be used as an interface. This should only define pure virtual methods to visit the two types: hospitalData and demogData 2) Modify placeData to also include a pure virtual function (so that derived classes can accept a visitor):

    //Lab05 anything that is place data must accept a visitor (aka must be visitable)
    virtual void accept(class Visitor &v) = 0;

3) Implement the accept method for hospitalData and demogData. It should just call visit on the visitor for the given type. 4) Define a visitorReport class that implements the visit method for each of the two types. For this week’s lab, the visit method just prints a subset of each type’s data (match example data) 5) Modify dataAQ.h to add a method to print a report of the data for any state that meets a given criteria. You must implement this by creating a visitorReport and calling accept with this visitor on a collection of demogData and hospitalData that meets the given criteria. (You may create the selection first then call accept on all values in the collection. The first report to create is for state data for any state with a percentage of the population below the poverty line above a threshold (stay tuned for additional reports):

void dataAQ::stateReport(double thresh);

An example output would include:

States with population below poverty line greater than 20%
*****print special report demog Data: 
Demographics Info (State): MS
Education info: 
(% Bachelor degree or more): 20.43
(% high school or more): 81.62
% below poverty: 22.63
*****print special report hospital data:
Hosptial Info: MS
Overall rating (out of 5): 2.57
*****print special report demog Data: 
Demographics Info (State): NM
Education info: 
(% Bachelor degree or more): 25.58
(% high school or more): 83.39
% below poverty: 20.40
*****print special report hospital data:
Hosptial Info: NM
Overall rating (out of 5): 2.73
-----Generated a report for a total of: 2

The visitor pattern is most useful with many differnt types and different types of visitors. We will play with these ideas next week.

Scoring ——– This lab is meant to be simple so is worth half credit. We will expand these technologies and do a more detailed re-design next week.
Autograding (stay tuned) 30
Code review/design matching lab spec 20