CS20006 Assignment 5 Solution

Important Notes
These assignments develop over Assignment 3 in the following ways:
1. Extends the specification by introducing information of passenger and booking category
2. Extends the requirements for an exception-safe design
3. Expands the design principles by mixing parametric polymorphism (templates for static time polymorphism) with polymorphic hierarchy (virtual functions for run-time polymorphism) for better type-safety, efficiency, flexibility, and code re-use.
4. Expects extensive use of STL for better quality, efficiency, and code re-use
5. Expects a proper multi-file code organization (with .h and .cpp files) for better code maintenance
6. Expects a more formal development process supported by UML, HLD, LLD, Test Plan, and Test Reprots
high
Much of the document is re-used from Assignment 3. New additions (to existing sections) or new sections are marked with * or light. Deletions are struck out as deleted. These are for ease of reading and understanding. However, the entire document should be carefully studied for fine details.
Explanatory Appendix B for Unit Testing has been omitted for brevity.

We need to develop a rudimentary railway reservation / booking system (somewhat like IRCTC Train Ticket Booking, but extremely scaled down in features). We present various stages of this development process leading finally to the specific tasks of the assignment.
1 Specification
This is the outline specification that has been acquired from the client.
1.1 Requirement Statement
The entities involved in the booking system design include:
• Station (Section 1.4.1): Every Station is identified by its name. Booking is done between any two Stations.
• Railways: It is the Indian railways. It has a collection of Stations with pairwise distance between Stations known a priori. Naturally, there can be only one Railways, called IndianRailways, in the system.
• BookingClass (Section 1.4.2): There are several BookingClasses for travel (as in Indian Railways fare classes explained). Each BookingClass has the following attributes:
– Name: Name of the BookingClass
– Seat / Berth: Whether the BookingClass provides sleeping berths or just seats. This will not change in future.
– AC / Non-AC: Whether BookingClass is air-conditioned or otherwise. This will not change in future. – # of Tiers: How many tiers exist in the coach for this BookingClass. This will not change in future.
Further, some BookingCategorys allow for priority booking (called Tatkal ) on a higher Tatkal fare depending on the BookingClass of travel and fare as given in the Talkal Charges Matrix in Section 1.4.3.
• *BookingCategory (Section 1.4.3): There are several BookingCategory for travel (as in IRCTC Book Ticket). Each BookingCategory has the following attributes:
– Name: Name of the BookingCategory
– Eligibility: Eligibility criteria / conditions for the BookingCategory – typically dependent on the
Passenger
Further,
– Some BookingCategorys allow for Concessional fare based on the BookingClass and the eligibility of the Passenger as given in the Booking Category Matrix and the Disability Concession Factor Matrix in Section 1.4.3.
– Some BookingCategorys allow for priority (Tatkal) booking on a higher Tatkal fare depending on the BookingClass of travel and fare as given in the Talkal Charges Matrix in Section 1.4.3.
• Booking (Section 1.3): A Booking is requested with the following information:
– fromStation: Station from which the travel starts for the Booking. This is given by the name of the Station
– toStation: Station at which the travel ends for the Booking. This is given by the name of the Station
– *bookingClass: BookingClass for the Booking. This is given from a set of available options (as if a drop-down menu, if the application were build with a GUI).
– *bookingCategory: BookingCategory for the Booking. This is given from a set of available options (as if a drop-down menu, if the application were build with a GUI).
On request of a Booking, the same is processed and fare is computed based on the business logic given in Section 1.3. The Booking is then confirmed with PNR and other details on the output. PNR is serially allocated starting with 1.
– name: Name of the passenger comprising (input as three separate strings):
∗ *firstName: Optional if lastName is present
∗ *middleName: Optional
∗ *lastName: Optional if firstName is present
– gender: Gender of the passenger: male or female – to be used for verification of identity and decisions about eligibility for a BookingCategory
– aadhaar #: 12-digit Aadhaar Number to be used as a unique ID and input as a string
– mobile #: 10-digit Mobile number (optional) and input as a string
– *disability type: Type of disability (optional)
– *disabilityID #: Number of the divyangjan ID (optional) and input as a string. This is used to check eligibility for Divyaang BookingCategory booking.
– category: One of General, Ladies, Senior Citizen, Divyaang, Tatkal, Premium Tatkal
1.2 Assumptions
The following assumptions are made for the design:
• IndianRailways has a given set of Stations with distances known a priori. The list of Stations and distances between them are given as Master Data in Section 1.4. No new station can be added to the IndianRailways and distance between pair of stations do not change.
• No passenger information is considered for the Booking
• *The booking system would always be in a consistent, well-defined state. All input data (of settable masters like Stations and distance, or Booking inputs etc.), should be validated for format, type, and consistency. All kinds of errors and exceptions in business logic and processing algorithm should also be handled properly.
1.3 *Business Logic
The fare between a pair of stations for a booking class is determined through the following steps:
• Base Fare: The base fare between two stations is computed by multiplying the distance between the stations with the base fare for every KM of travel. The base fare applies to the Sleeper booking class.
• No concession is allowed for Tatkal booking (in Tatkal and PremiumTatkal categories). For a Tatkal booking, a premium is charged on the base fare (as shown in Section 1.4.3) capped by minimum and maximum amounts and minimum distance of travel. After adding this premium, the loading for the booking class is applied as before (Section 1.4.2).
The premium is double of Tatkal for every PremiumTatkal booking.
• Finally, a reservation charge is added to the fare depending on the class of travel (Section 1.4.2).
• Final fare is rounded to the nearest integer.
• dateOfBooking has no effect on the fare.
• Passenger has no effect on the fare as it is being ignored for now.
1.3.1 Example: Booking Category = General For a booking from Delhi to Mumbai:
By AC3Tier:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for AC3Tier = Rs. 723.50 * 2.50 = Rs. 1808.75
• After adding the reservation charge, we get Rs. 1808.75 + Rs. 40.00 = Rs. 1848.75 ≈ Rs. 1849/=
(rounded)
By ACFirstClass:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for ACFirstClass = Rs. 723.50 * 6.50 = Rs. 4702.75
• After adding the reservation charge, we get Rs. 4702.75 + Rs. 60.00 = Rs. 4762.75 ≈ Rs. 4763/=
(rounded)
1.3.2 Example: Booking Category = Senior Citizen For a booking from Delhi to Mumbai:
By AC3Tier for Male:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for AC3Tier = Rs. 723.50 * 2.50 = Rs. 1808.75
• Concession fare = Rs. 1808.75 * (1.00 - 0.40) = Rs. 1085.25
• After adding the reservation charge, we get Rs. 1085.25 + Rs. 40.00 = Rs. 1125.25 ≈ Rs. 1125/=
(rounded)
By ACFirstClass for Female:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for ACFirstClass = Rs. 723.50 * 6.50 = Rs. 4702.75
• Concession fare = Rs. 4702.75 * (1.00 - 0.50) = Rs. 2351.375
• After adding the reservation charge, we get Rs. 2351.375 + Rs. 60.00 = Rs. 2411.375 ≈ Rs. 2411/= (rounded)
1.3.3 Example: Booking Category = Divyaang For a booking from Delhi to Mumbai:
By AC3Tier for Blind:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for AC3Tier = Rs. 723.50 * 2.50 = Rs. 1808.75
• Concession fare = Rs. 1808.75 * (1.00 - 0.75) = Rs. 452.1875
• After adding the reservation charge, we get Rs. 452.1875 + Rs. 40.00 = Rs. 492.1875 ≈ Rs. 492/= (rounded)
By ACFirstClass for Cancer Patient:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for ACFirstClass = Rs. 723.50 * 6.50 = Rs. 4702.75
• Concession fare = Rs. 4702.75 * (1.00 - 0.50) = Rs. 2351.375
• After adding the reservation charge, we get Rs. 2351.375 + Rs. 60.00 = Rs. 2411.375 ≈ Rs. 2411/= (rounded)
1.3.4 Example: Booking Category = Tatkal For a booking from Delhi to Mumbai:
By AC3Tier:
• Distance from Delhi to Mumbai = 1447km
• Base fare = 1447km * Rs. 0.5 / km = Rs. 723.50
• Loaded fare for AC3Tier = Rs. 723.50 * 2.50 = Rs. 1808.75. This is the basic fare to be used computing tatkal charge
• 30% of basic fare = Rs. 1808.75 * 0.30 = Rs. 542.625
• Tatkal charge = Rs. 400.00 (by maximum cap)
• After adding the reservation charge, we get Rs. 1808.75 + Rs. 400.00 Rs. 40.00 = Rs. 2248.75 ≈ Rs. 2249/= (rounded)
For a booking from Chennai to Bangalore:
By ACFirstClass:
• Distance from Chennai to Bangalore = 350km
• Base fare = 350km * Rs. 0.5 / km = Rs. 175.00
• Loaded fare for ACFirstClass = Rs. 175.00 * 6.50 = Rs. 1137.50
• 30% of basic fare = Rs. 1137.50 * 0.30 = Rs. 341.25
• Tatkal charge = Rs. 0.00 (by minimum distance cap)
• After adding the reservation charge, we get Rs. 1137.50 + Rs. 0.00 + Rs. 60.00 = Rs. 1197.50 ≈ Rs. 1198/= (rounded)
1.4 Master Data
While it will be nice to read the master data from master files at the start of the system run, it will be fine to hard-code these data for this assignment. However, the hard-coding should be done in limited, well-documented areas of the code so that it will be easy to change them as needed. These should be not hard-code inside the implementation of functions / methods.
1.4.1 Stations
IndianRailways has five Stations, namely: Mumbai, Delhi, Bangalore, Kolkata, and Chennai. The distances between the stations are given below:
Station Distance Matrix
From
Station To Station
Mumbai Delhi Bangalore Kolkata Chennai
Distance in KM
Mumbai X 1447
Mumbai 981
Mumbai 2014
Mumbai 1338
Delhi X 2150
Delhi 1472
Delhi 2180
Bangalore X 1871
Bangalore 350
Kolkata X 1659
Distance between a pair of stations is symmetric
1.4.2 Booking Classes
IndianRailways has eight booking classes as follows - shown with their respective attributes:
*Booking Class Matrix
Booking Class Name *Fare Seat / AC # Luxury / *Reservation
Load Berth of Ordinary Charge
Factor Tiers (in Rs.)
ACFirstClass AC 6.50 Berth Yes 2 Luxury 60.00
(1A) First Class
*ExecutiveChairCar Executive
Chair Car 5.00 Seat Yes 0 Luxury 60.00
AC2Tier AC 4.00 Berth Yes 2 Ordinary 50.00
(2A) 2 Tier
FirstClass First 3.00 Berth No 2 Luxury 50.00
(FC) Class
AC3Tier AC 2.50 Berth Yes 3 Ordinary 40.00
(3A) 3 Tier
ACChairCar AC 2.00 Seat Yes 0 Ordinary 40.00
(CC) Chair Car
Sleeper
(SL) Sleeper 1.00 Berth No 3 Ordinary 20.00
SecondSitting Second 0.60 Seat No 0 Ordinary 15.00
(2S) Sitting
• Seat / Berth & AC / non-AC classification, and # of tiers will not change in future
• IRCTC Book Ticket
• Indian Railways fare classes explained
1.4.3 *Booking Categories
Tickets can be booked in the IndianRailways in one of six categories have the respective attributes:
Booking Category Matrix
Booking Name Concession Remarks
Category Factor
General General 0.00 General booking available to all
Ladies Ladies 0.00 Special booking for ladies and 12− years male
Applies for berth priority. No fare concession
SeniorCitizen Senior Citizen 0.40 Special booking for 60+ years male
0.50 Special booking for 58+ years female
Divyaang Divyaang - Special booking for the disabled
as charged by Disability Concession Matrix
Tatkal Tatkal 0.00 Priority booking 1 day before travel as charged by Tatkal Charges Matrix
PremiumTatkal Premium Tatkal 0.00 Priority booking 1 day before travel as charged by Tatkal Charges Matrix
• Rail Fare Concession for Senior Citizens
• Rail Fare Concession for Disabled Persons
Disability Concession Factor Matrix
Booking Class Type of Disability
Blind Orthopaedically Cancer TB
Handicapped Patients Patients
ACFirstClass 0.50 0.50 0.50 0.00
ExecutiveChairCar 0.75 0.75 0.75 0.00
AC2Tier 0.50 0.50 0.50 0.00
FirstClass 0.75 0.75 0.75 0.75
AC3Tier 0.75 0.75 1.00 0.00
ACChairCar 0.75 0.75 1.00 0.00
Sleeper 0.75 0.75 1.00 0.75
SecondSitting 0.75 0.75 1.00 0.75
• Rail Fare Concession for Disabled Persons
• Concession Rules
Talkal Charges Matrix
Booking Class Minimum Maximum Minimum
Tatkal Charges Tatkal Charges Distance for charge
(in Rs.) (in Rs.) (in Km)
ACFirstClass 400.00 500.00 500
ExecutiveChairCar 400.00 500.00 250
AC2Tier 400.00 500.00 500
FirstClass 400.00 500.00 500
AC3Tier 300.00 400.00 500
ACChairCar 125.00 225.00 250
Sleeper 100.00 200.00 500
SecondSitting 10.00 15.00 100
• The Tatkal Charges have been fixed as a percentage of fare at the rate of 10% of basic fare for second class (SecondSitting) and 30% of basic fare for all other classes subject to minimum and maximum as given above • A Premium Tatkal ticket has same charge rules as above but is charged at double of Tatkal
• No tatkal charge is levied for travel below the minimum distance for charge
• Indian Railways Tatkal Scheme
2 *Analysis of Specification
As discussed in SDLC and UML, the first target in analysis is to extract the Use Case and Class diagrams for the system. Then build the other diagrams – Sequence, Communication, Activity, and State Machine.
2.1 *Use Case Diagram
We first analyze the specifications to identify the actors, use-cases, and the relationships in the problem. We also try to extract possible constraints on the design. Identification of the actors and use-cases for Use-Case Diagrams is left as a part of assignment exercise.
2.2 *Class Diagram
Next we need to identify the classes, attributes, methods, hierarchy, associations, relationships etc. to prepare the Class Diagram. While the overall and detailed Class Diagram will be left as an exercise in the assignment, we analyze to identify the classes and discuss various aspects of the classes to facilitate the process of design.
Our implementation language is pre-decided to be C++. So during analysis, we leave appropriate pointers for HLD and LLD in the context of C++. This is help in the translation of the Class Diagram into the C++ classes.
2.2.1 Summary of Polymorphisms in C++
Before delving into the actual task we present a summary of polymorphisms available in C++ (as was also discussed in the class). We shall make regular references to these.
C++ support the following four kinds of polymorphism.
• Ad-hoc Polymorphism: Static polymorphism by overloading of methods. Available globally or on a non-virtual hierarchy (inheritance without virtual functions).
• Inclusion Polymorphism: Dynamic polymorphism by overriding of methods on a polymorphic hierarchy (inheritance with virtual functions)
• Parametric Polymorphism: Static polymorphism by templates where type is used as parameter. This is using template meta-programming.
This is often combined with Inclusion Polymorphism.
• Coercion Polymorphism: Type casting. This would be grossly avoided.
2.2.2 Classes in Booking Software
We identify entities from the specification as classes. Also, we extract some abstract concepts as classes as we factor and normalize for our design.
• *Class Station
Station is a simple data class with unique name.
• *Class and Hierarchy of Gender
Gender is a simple type with Male and Female type constants or sub-types. For uniformilty of design, we can model it by inclusion and parametric polymorphism with Gender being an abstract base class.
• *Class Railways
Class Railways should be a singleton and should contain the master data of stations and distances. The singleton should be constant as no station can be added and distances cannot be changed. Further, it needs to exclude duplication of Station and Station to Station distances.
• *Class and Hierarchy of BookingClasses
*BookingClass needs redesign based on our experience in Assignment 3. It can be made more compact and reuseable.
If multiple properties are used in organizing the hierarchy, then the model would need multiple inheritance. However, we do not want to use multiple inheritance for the associated complications and inefficiency. Rather, we would use single inheritance on the strongest property and use the rest as HAS-A with polymorphic value based on the leaf class.
Naturally, there can be two candidates for this as Fare Load Factor, # of Tiers, and Luxury / Ordinary are more like pure attributes and clearly not useful for hierarchy:
– AC or Non-AC: Air-condition leads to comfort level, and is not fundamental to travel. So this is a weak candidate.
– Seat or Berth: This is fundamental property for a rail travel. So this is a strong candidate.
The hierarchy should be extensible in future as new booking classes are added.
– Tatkal Load Factor: The factor by which premium is charged for the BookingClass.
– Minimum (Maximum) Tatkal Charge: Minimum (Maximum) Tatkal charge for the BookingClass.
– Minimum Tatkal Distance: Minimum distance of travel to levy Tatkal charge for the BookingClass.
• *Class and Hierarchy of BookingCategory
Here we come across an interesting issue. Regarding the role of BookingCategory in terms of determination of fare. How should we handle the general, concessional, and priority booking categories?
– General Booking has neither any concession nor any premium charge
– Concessional Booking has concessions based on a mix factors from BookingCategory, Booking-
Class, and gender, age & ability type (divyaangjan) of the Passenger
– Priority Booking attracts Tatkal charge depending on BookingClass and distance.
It will be quite interesting to depict this information through Associations and Relationships in the UML Class Diagram and is left as an exercise.
While General Booking does not need any additional support, both concessional and priority booking would need further information representation and polymporphic computation.
So we can clearly see that we need to acknowledge Concessions and Divyaang (Disability) as key abstract concepts with appropriate polymorphic behavior to complete the modeling of BookingCategory.
– Priority Booking: In contrast to above, Tatkal charges depend on the BookingClass and can be subsumed in it by normalization . Hence, we simply add the data members in BookingClass above.
• *Class and Hierarchy of Divyaang (Disabled)
• *Class and Hierarchy of Concessions
Concessions class based on
BookingCategory Dependency on class Remarks
BookingClasses Passenger Divyaang
General No No No No concession
Ladies No Yes No No concession for now
SeniorCitizen No Yes No Concession based on gender
Divyaang Yes Yes Yes Concession as in matrix
Tatkal categories are not considered as there is no concession
Clearly, no common interface can compute (extract) the concession across different Concessions classes in the hierarchy as specialized from a base class Concessions. So we need to model it by flat single level ad-hoc polymorphism and there is no logical scope to use inclusion or parametric polymorphism. Consequently, the base class cannot be abstract either.
• *Class and Hierarchy of Booking
*In assignment 3, Booking could be a simple concrete class because there was only one algorithm (business logic) to compute fare that used some attribute values of the respective BookingClass. The model now has to improve, because the business logic of Booking depends on the BookingCategory.
So Booking can be an abstract base class rooting an inclusion and parametric polymorphic hierarchy that parallels the hierarchy of the BookingCategory.
• *Class and Hierarchy of Passenger
*The Passenger class is a simple data class that needs to keep data member values as specified. Of course, it will need a number of validation methods for the constraints specified for its data members like name, age, aadhaar (syntax only), etc.
• *Class and Hierarchy of Exceptions
Since erroneous inputs and conditions are allowed now, we need to design a hierarchy of Exceptions classes derived from std::exception.
Fundamentally, we can identify the following top level Exceptions types:
This is used by several classes.
This should be caught in the application.
This should be caught in the application.
This should be caught in the application.
2.3 *Sequence, Communication, Activity & State Machine Diagrams
Left as a part of assignment exercise.
3 High Level Design
Based on the analysis, now we carry out the High Level Design (HLD) below for Classes, Interfaces, Constants, Statics, Exceptions, and overall design considerations.
3.1 Design Principles
• Flexible & Extensible Design
– The design should be flexible. That is, it should be easy to change the changeable parameters (like base rate, load factor etc.) easily from the Application space. This should should not need re-building of the library of classes.
– The design should be extensible. That is, it should be easy to add new behaviour (classes) wherever indicated in the specification (like Booking Classes, Booking, Passenger, etc.). This should not require a re-coding of the existing applications.
• Minimal Design
– Only the stated models and behaviour should be coded. No extra class or method should be coded.
– Less code, less error principle to be followed.
• *Reliable & Safe Design
– Reliability should be a priority. Everything should work as designed and coded.
– Data members, methods and objects should be made constant wherever possible.
– Parameters should be appropriately defaulted wherever possible
– The system should never be allowed to go into an inconsistent state.
– All possible errors of data and processing must be appropriately thrown and caught handled.
• Testable Design
– Every class should support the output streaming operator for checking intermittent output if needed.
– Every class should be tested with an appropriate test application for its unit functionality (Section 6.1).
– Test Applications (Section 6.2) and regression test suites should be designed for testing the application on (at least) the common scenarios of use.
3.2 *Classes
*The classes and hierarchy as outlined in Requirement Specification (Section 1.1) and Analysis (Section 2), can be put in HLD.
• Class Station HAS-A name.
• Class Railways is a singleton called IndianRailways. It has a collection of the Stations and their mutual distances. IndianRailways is a constant object.
Booking should support Passenger as a null-able parameter for future extension.
3.2.1 Modeling Sub-Types
During the analysis, we see that there are number of classes and sub-classes including Gender, BookingClass, BookingCategory, and Divyaang where static sub-typing exists as the sub-classes mostly have the same set of data members and methods. Even the Booking can be modeled with this. Specifically, we observe the following:
1. Data members are constants at many places and takes by static values (specific to the sub-class).
2. Methods are mostly identical in algorithm and differ in static data.
3. In a number of cases, methods need to be invoked by dynamic dispatch to support a uniform type interface in the application.
4. Conceptually, in most cases, a single-level flat hierarchy with an abstract base class and concrete subclasses suffice the representation.
5. Most of the classes also represent static concepts. Hence, it is desirable that only a single constant object of the class should be constructed that can represent the type and be used as a placeholder everywhere for type consistency.
This leads to the question of which form/s of polymorphism in C++ should we use to model the hierarchy. Note that we have already decided to use a static hiearchy with ad-hoc polymorphism for Concessions.
If we use inclusion polymorphism, we have a greater flexibility for hierarchy along with dynamic dispatch based on the sub-class type, but the code bloats. This is good for (3), (4) & (5), but not (1) & (2).
If we use parametric polymorphism, it is relatively difficult to have flexible hierarchy or have dynamic dispatch, but we can have a more compact code with better reuse (and less code to actually write). This is good for (1), (2) & (5), but not (3) & (4).
By Inclusion Polymorphism We code Gender as follows:
Header File
// Gender.h
#ifndef __GENDER_H
#define __GENDER_H
#include <string> using namespace std;
// Abstract Base Class - Concept of Gender class Gender { const string& name_; // Name of the gender
protected:
Gender(const string& name) : name_(name) { } virtual ~Gender() { }
public: const string& GetName() const { return name_; } virtual const string GetTitle() const = 0; // Salutation specific to gender
static bool IsMale(const Gender&); // Checking and matching gender
};
// Male class - specialized gender class Male : public Gender { Male() : Gender(Male::sName) {} static const string sName; // Name "Male" for this gender sub-type
public:
return theObj;
}
const string GetTitle() const // Dynamic dispatch
};
// Female class - specialized gender class Female : public Gender { Female() : Gender(Female::sName) { }
static const string sName; // Name "Female" for this gender sub-type
public:
return theObj;
}
const string GetTitle() const // Dynamic dispatch
};
inline bool Gender::IsMale(const Gender& g) { return &g == &Male::Type(); } #endif // __GENDER_H
Note that there is significant duplication of code between Male and Female class codes.
Source File
// Gender.cpp
#include <string>
using namespace std;
#include "Gender.h"
// Names defined as static constants const string Male::sName = "Male"; const string Female::sName = "Female"; We are now ready to use the above classes.
Application File
// Gender_App.cpp #include <string> using namespace std; #include "Gender.h"
class Person { const string name_; const Gender& gender_; public:
Person( const string& name, const Gender& gender) : // Singleton constant Gender sub-class object name_(name), gender_(gender) {}
friend ostream& operator<<(ostream& os, const Person& p) { os << p.gender_.GetTitle() << " " // Dynamic dispatch based on gender type << p.name_ << " is a " // Name set for the Person
<< p.gender_.GetName() // Static dispatch on Gender to get the
// name of the gender << endl; return os;
}
};
int main() {
Person p1("Ramen Bag",
Male::Type()); // Type-safe expression of Male
Person p2("Elisa Tang",
Female::Type()); // Type-safe expression of Female
cout << p1; cout << p2;
return 0;
}
Output:
Mr. Ramen Bag is a Male
Ms. Elisa Tang is a Female
By Parametric Polymorphism
Now we code Gender as follows using parametric polymorphism with inclusion polymorphism:
Header File
#ifndef __GENDER_H
#define __GENDER_H
#include <string> using namespace std;
// Forward declaration of templatized class template<typename T> class GenderTypes; // Generic Gender type to generate specific genders
// Generic gender type class Gender { // Abstract Base Class const string& name_; // Name of the Gender
// Tag types - to instantiate the template
// Note that these names are placeholders only and are not exposed outside the class // Also they are put inside the class for not cluttering the global namespace struct MaleType {}; struct FemaleType {};
protected:
Gender(const string& name) : name_(name) {} virtual ~Gender() { }
public: const string& GetName() const { return name_; } virtual const string GetTitle() const = 0; // Salutation specific to gender static bool IsMale(const Gender&); // Checking and matching gender
// Enumerated types - the target sub-types typedef GenderTypes<MaleType> Male; typedef GenderTypes<FemaleType> Female;
};
// Specific gender types template<typename T> class GenderTypes : public Gender { static const string sName; // Respective name of the gender static const string sSalutation; // Respective salutation for the gender
GenderTypes(const string& name = GenderTypes<T>::sName) : Gender(name) { }
~GenderTypes() { }
public:
return theObject;
}
const string GetTitle() const // Dynamic dispatch
{ return GenderTypes<T>::sSalutation; } // Salutation parametrized by static
};
inline
bool Gender::IsMale(const Gender& g) { return &g == &Gender::Male::Type(); }
#endif // __GENDER_H
#endif // __GENDER_H
Note that the earlier duplication of code between Male and Female class codes are now removed and refactored into the template code. It improves code reuse. In this small example, however, the reduction in LoC is not visible (actually it bloats). When we have more sub-classes, like for BookingClass, we shall have significant code reduction and reuse.
Source File
// Gender.cpp
#include <string> using namespace std;
#include "Gender.h"
// Names defined as static constants const string Gender::Male::sName = "Male"; const string Gender::Female::sName = "Female";
// Salutations defined as static constants const string Gender::Male::sSalutation = "Mr."; const string Gender::Female::sSalutation = "Ms.";
Application File
Note that only change in the application is in the scoping of the sub-types as Male (Female) becomes Gender::Male (Gender::Female). This is even more type-safe as the global namespace is not cluttered.
// Gender_App.cpp
#include <iostream> #include <string> using namespace std; #include "Gender.h"
class Person { const string name_; const Gender& gender_; public:
Person( const string& name, const Gender& gender) : // Singleton constant Gender sub-class object name_(name), gender_(gender) {}
friend ostream& operator<<(ostream& os, const Person& p) { os << p.gender_.GetTitle() << " " // Dynamic dispatch based on gender type << p.name_ << " is a " // Name set for the Person
<< p.gender_.GetName() // Static dispatch on Gender to get the
// name of the gender << endl; return os;
}
};
int main() {
Person p1("Ramen Bag",
Gender::Male::Type()); // Type-safe expression of Male - note the change in scoping
Person p2("Elisa Tang",
Gender::Female::Type()); // Type-safe expression of Female - note the change in scoping
cout << p1; cout << p2;
return 0;
}
Output:
Mr. Ramen Bag is a Male
Ms. Elisa Tang is a Female
3.2.2 Virtual Construction Idiom
We know that constructor for a class is static and it cannot be virtual. But conceptually, we come across such situations often when we need to choose between a set of sub-classes based on the information of some other types. For example, there are as many Booking sub-classes as there are BookingCategorys - one for each. Now given a BookingCategory in the input, how do we invoke the constructor of the right sub-class of Booking. The situation is again that of a type-switch, except here based on the type of one hierarchy (BookingCategory), we need to create an appropriate object of another (Booking) hierarchy. Notionally, we need to virtualize the construction process. A naive solution would be to explicitly check the type of BookingCategory object, and create corresponding Booking class object which suffers from the usual evils of being type unsafe.
Let us consider a tiny example to understand the problem and the solution. Consider an application for a Swimming Pool Slot booking where separate slots (and pools) based on gender. So we have a PoolSlot abstract class with MalePoolSlot FemalePoolSlot as respective specializations. We use our earlier design of Gender and produce the following code using an explicit type-switch in PoolSlot::ReservePoolSlot() function:
#include <iostream> #include <string> using namespace std;
class Gender { const string& name_;
protected:
Gender(const string& name) : name_(name) { } virtual ~Gender() { }
public:
const string& GetName() const { return name_; } static bool IsMale(const Gender&); // In a good OOP design we must not have / // need such an interface!
};
class Male : public Gender { Male() : Gender(Male::sName) {} static const string sName;
public:
static const Gender& Type() { static const Male theObj; return theObj;
}
};
class Female : public Gender { Female() : Gender(Female::sName) { } static const string sName;
public:
static const Gender& Type() { static const Female theObj; return theObj;
}
};
// Explicit checking of type bool Gender::IsMale(const Gender& g) { return &g == &Male::Type(); } // Names defined as static constants const string Male::sName = "Male"; const string Female::sName = "Female";
class PoolSlot { protected:
const string name_;
PoolSlot(const string& name) : name_(name) { } public:
~PoolSlot() {} static PoolSlot* ReservePoolSlot(const string& name, const Gender& g);
};
class MalePoolSlot : public PoolSlot { public:
MalePoolSlot(const string& name) : PoolSlot(name) { cout << "MalePoolSlot created for " << name_ << endl; } };
class FemalePoolSlot : public PoolSlot { public:
FemalePoolSlot(const string& name) : PoolSlot(name) { cout << "FemalePoolSlot created for " << name_ << endl; }
};
PoolSlot* PoolSlot::ReservePoolSlot(const string& name, const Gender& g) {
PoolSlot* p = 0;
// This is the type-switch that we must avoid // This is error-prone, not scalable, and type-unsafe if (Gender::IsMale(g)) p = new MalePoolSlot(name);
else p = new FemalePoolSlot(name);
return p;
}
int main() {
PoolSlot* p1 = PoolSlot::ReservePoolSlot("Ramen Bag", Male::Type()); PoolSlot* p2 = PoolSlot::ReservePoolSlot("Elisa Tang", Female::Type());
delete p1; delete p2;
return 0;
}
Now we refine the design:
1. Drop the explicit type-checking function Gender::IsMale().
2. Introduce a virtual function Gender::CreatePoolSlot() for dynamically switching type based on gender 3. Replace explicit type-switch in PoolSlot::ReservePoolSlot() by dynamic dispatch on gender type
4. Construct appropriate type of PoolSlot object on overridden versions of Male::CreatePoolSlot() and Female::CreatePoolSlot() respectively.
#include <iostream>
#include <string> using namespace std; class PoolSlot;
class Gender { const string& name_;
protected:
Gender(const string& name) : name_(name) { } virtual ~Gender() { }
public:
const string& GetName() const { return name_; } //static bool IsMale(const Gender&); virtual PoolSlot* CreatePooSlot(const string& name) const = 0;
};
class Male : public Gender { Male() : Gender(Male::sName) {} static const string sName;
public:
static const Gender& Type() { static const Male theObj; return theObj;
}
PoolSlot* CreatePooSlot(const string& name) const;
};
class Female : public Gender { Female() : Gender(Female::sName) { } static const string sName;
public:
static const Gender& Type() { static const Female theObj; return theObj;
}
PoolSlot* CreatePooSlot(const string& name) const ;
};
//bool Gender::IsMale(const Gender& g) { return &g == &Male::Type(); }
// Names defined as static constants const string Male::sName = "Male"; const string Female::sName = "Female";
class PoolSlot { protected:
const string name_;
PoolSlot(const string& name) : name_(name) { } public: ~PoolSlot() {}
static PoolSlot* ReservePoolSlot(const string& name, const Gender& g);
};
class MalePoolSlot : public PoolSlot { public:
MalePoolSlot(const string& name) : PoolSlot(name) { cout << "MalePoolSlot created for " << name_ << endl;
}
};
// Creates MalePoolSlot object
PoolSlot* Male::CreatePooSlot(const string& name) const { return new MalePoolSlot(name);
}
class FemalePoolSlot : public PoolSlot { public:
FemalePoolSlot(const string& name) : PoolSlot(name) { cout << "FemalePoolSlot created for " << name_ << endl; }
};
// Creates FemalePoolSlot object
PoolSlot* Female::CreatePooSlot(const string& name) const { return new FemalePoolSlot(name);
}
PoolSlot* PoolSlot::ReservePoolSlot(const string& name, const Gender& g) {
//PoolSlot* p = 0;
//if (Gender::IsMale(g))
// p = new MalePoolSlot(name);
//else
// p = new FemalePoolSlot(name);
//return p;
// Dynamic dispatch takes care of the type switch on gender return g.CreatePooSlot(name);
}
int main() {
PoolSlot* p1 = PoolSlot::ReservePoolSlot("Ramen Bag", Male::Type()); PoolSlot* p2 = PoolSlot::ReservePoolSlot("Elisa Tang", Female::Type());
delete p1; delete p2;
return 0;
}
Effectively, we achieve virtualization in construction based on an object hierarchy. However, the cost is - the design of the Gender now gets tightly coupled with the design of PoolSlot (which should not have been). There would the work arounds for that too - but that’s later.
So now we are ready to do a good design for Booking class hierarchy.
3.3 Interfaces
*The interfaces, as outlined in Requirement Specification (Section 1.1) and Analysis (Section 2), can be put in HLD.
• Constructors / Destructors: Proper constructor and destructor for every class
• Copy Functions: Provide user-defined Copy Constructor and / or Copy Assignment Operator for a class if used in the design (should not be needed). Otherwise, block them.
• Provide output streaming operator for every class to help output process as well as debugging
• Class Station to have GetName() for accessing its name and GetDistance(.) to get distance to another station.
• Class Railways to have GetDistance(., .) to get distance between a pair of stations. It should also have proper interface for making it a singleton IndianRailways
• Class Booking to have ComputeFare() to implement the fare computation logic. Should it be virtual (polymorphic) for future extensions?
• *Make methods const wherever possible.
3.4 Constants
*Various static constants as outlined in Requirement Specification (Section 1.1), Master Data (Section 1.4), and Analysis (Section 2), can be put in HLD.
The following should be static constants in appropriate classes:
• Load Factors of various BookingClasses
• Base Fare Rate: Rs. 0.50 / km
• AC Surcharge: Rs. 50.00
• Luxury Tax: 25% on booking amount
3.5 Statics
*Various static data members as outlined in Requirement Specification (Section 1.1), Master Data (Section 1.4), and Analysis (Section 2), can be put in HLD.
• Class Railways to have sStations (list of stations) and sDistStations (distance between stations).
• Class BookingClasses to have load factors.
• Class Booking to have sBaseFarePerKM, sBookings (list of bookings done), sBookingPNRSerial (next available PNR), sACSurcharge, and sLuxuryTaxPercent
3.6 *Errors & Exceptions
– name cannot be empty
– No duplicate Station name would be allowed
– Distance must be defined between every pair of Stations. The definition is considered symmetric so only one direction should given.
– No duplicate distance definition is allowed
– Distance between two same Stations is not allowed
– dateOfBirth must precede dateOfReservation.
– gender must be male or female. It must be valid by input. That is, it should not be possible to input a wrong gender.
– aadhaar # is 12 digit. It should be validated for absence of non-digit and length.
– mobile # is 10 digit. It should be validated, if provided, for absence of non-digit and length.
– disability type must be valid by input.
– disabilityID #: Number of the divyangjan ID (optional)
– fromStation and toStation must be valid (pre-existing). The distance between them must be pre-set. – dateOfBooking must be later than dateOfReservation and within one year from it.
– bookingClass must be valid by input. That is, it should not be possible to input a wrong bookingClass to the request.
– bookingCategory must be valid by input. That is, it should not be possible to input a wrong bookingCategory to the request.
– passenger data must be consistent with the bookingCategory.
– All valid booking requests can be served.
• BookingClass, BookingCategory, Concessions, and Divyaang are constructed from static data and can be assumed to be free of errors.
– Every error must be properly handled and meaningfully reported.
– If there are more than one validation failures, the system should attempt to report as many of them as possible in a single run.
– All validations and reporting should be based on exceptional design clearly separating the normal flow from the exception flow.
• There is no error in input, processing, or output.
• No error or exception handling to be incorporated in the design for this assignment. However, structure the code flow well so that they can be incorporated later with minimal changes (adhering to the need of flexibility).
4 Low-Level Design
Based on the High Level Design (HLD), we now perform the Low Level Design (LLD). LLD makes use of the specific constructs and idioms of C++.
4.1 Design Principles
• Encapsulation
– Maximize encapsulation for every class
– Use private access specifier for all data members that are not needed by derived classes, if any. Use protected otherwise.
– Use public access specifier for interface methods and static constants and friend functions only.
• STL Containers
– Use STL containers (like vector, map, hashmap, list, etc.) and their iterators. Do not use arrays – Use iterators for STL containers. Do not use bare for loops.
• Pointers & References
– Minimize the use of pointers. Use pointers only if you need null-able entities
– If you use pointer for dynamically allocated objects (should be minimized), remember to delete at an appropriate position.
– Use const reference wherever possible.
4.2 Design of Classes, Data Members & Methods
This is left as an exercise in the assignment. Design based on the HLD and the principles and document well.
5 Implementation
After completing the LLD, we perform the coding (implementation). In this we adhered to a set of basic guidelines and code organization.
5.1 Basic Coding Guidelines
5.2 *Code Organization
Ideally, the definition of every class (or hierarchy) should be put in a corresponding .h file with the static definitions and method implementations in the respective .cpp. The application should be in Application.cpp file. However, for simplicity, it would be acceptable if all the codes are put in the Application.cpp file with the application.
The code should be properly organized according to the following guidelines:
1. Every major class <classname>, and the hierarchy related to it, should be written in header file classname.h. Small and frequently invoked methods should also be inlined in this file.
2. The source or implementation file classname.cpp will contain the static definitions and remaining methods.
6 Test Plan
We also need to prepare a test plan to test the implementation at different stages of development so that better quality and productivity can be ensured. Variety of test processes are common. We shall follow two of these in the current assignment.
6.1 Unit Tests
For the purpose of understanding, in Section ?? we illustrate the test plan and test function for a few unit cases for the Fraction class we have developed in Assignment 2.
6.2 Application Test
After the units have been tested, we integrate them into the application and test various scenarios for the application. A sample test application was provided for the Fraction class in Assignment 2. However, since it was just a single class application, the application code looked pretty much like the unit test application code with the exception of the comparison with golden data.
Like the units, we again need to enumerate scenarios for the application in the test plan and write the application test.
In addition, a sample test application for booking is given in Section ?? with the expected output in Section ??. Your codes should pass this test application too.
7 Tasks
7.1 Assignment 4: UML Diagrams: Analysis & Design Phases
The following tasks are to be completed for the assignment:
1. UML Diagrams: Study the specifications of the booking system, and the analyses & design as discussed above to prepare the final analysis cum design document UML.pdf with the following Diagrams:
• Use Case Diagram: Identify the actors, use-cases & relationships.
• Class Diagram: Show the classes (with properties & operations), relationships & associations.
• Sequence Diagram: Depict the lifelines, messages & interaction fragments.
• Communication Diagram: Depict the frames, lifelines & messages.
• Activity Diagram: Model the activities, edges, controls, objects & actions.
• State Chart Diagram: Appropriately define the state machine for the problem.
• Note:
– Use annotations liberally in the diagrams as needed. Add more notes in the document to explain the diagrams as appropriate.
– You need to model handling of errors wherever needed, however, do not model exceptions as these are specific to C++.
2. Analysis & Design: Complete the HLD and the LLD in C++. Document the salient points from your design in Design.txt / Design.pdf. Follow the quality guidelines and design principles outlined above.
• Note:
– Necessary parts of HLD and all of LLD should be for C++.
– Design of every class (and hierarchy) should detail the non-static & static data members, nonstatic & static methods with const-ness and polymorphism as applicable.
– Exceptions should be modeled.
3. Bundle and Submissions: Name and bundle your files as given in Section 8 and submit to Moodle.
7.2 Assignment 5: Test Plan, Implementation & Test Report
The following tasks are to be completed for the assignment:
1. Implementation: Implement the LLD in C++ following the basic coding guidelines (Section A).
2. Test Planning: Write a unit test and application test plan in Testplan.txt covering all scenarios. Also, write the test suite with a couple of test cases for every scenario and golden output. Note that all wrong input or erroneous data situations are to be handled. Hence, the test plan and suite must cover positive and negative tests both.
3. Testing & Test Report: Implement unit test and application test codes and perform testing. Based on the test plan and suite, generate the PASS/FAIL report.
4. Bundle and Submissions: Name and bundle your files as given in Section 8 and submit to Moodle.
8 Submission of Files
8.1 Assignment 4: UML Diagrams: Analysis & Design Phases
The following files must be submitted as a single ZIP file:
1. UML.pdf: Use Case, Class and Sequence, Communication, Activity & State Machine Diagrams, annotations, notes.
2. Design.txt / Design.pdf: The design document stating the design details (especially LLD) with principles and guidelines followed
Every file must have your name and roll number.
8.2 Assignment 5: Test Plan, Implementation & Test Report
The following files must be submitted as a single ZIP file:
1. Documents.zip
(a) Testplan.txt / Testplan.pdf: The test plan document stating scenarios for unit tests and of the test application, and test cases (with golden output).
(b) Testreport.txt / Testreport.pdf: The test report document based on the test plan and suite showing PASS / FAIL of test cases.
2. Source.zip:
(a) Source (.cpp) and header (.h) files for classes.
(b) Source (.cpp) and header (.h) files for test applications.
(c) README file that describes the contents of every file in the Source.zip. Also, mention the compiler (with version, and compiler options, if any) that you have used.
3. Outputs.zip
(a) Output from the your test application developed from the test plans
• The output file can be generated by redirecting the output to a text file or by copy-paste from the console in a text file.
• There is no need to include the a.out file.
(b) Both positive as well as negative outputs must be shown.
Every file (with the exception of program output) must have your name and roll number.
9.1 Assignment 4: UML Diagrams: Analysis & Design Phases
UML
Breakup [60]
Use Case Diagram [5]
Class Diagram [20]
Sequence Diagram [10]
Communication Diagram [5]
Activity Diagram [15]
State Machine Diagram [5]
Design
Breakup [40]
Design of Station & Railways Classes [4]
Design of BookingClass Class & Hierarchy [5]
Design of Divyaang Class & Hierarchy [3]
Design of Concessions Class & Hierarchy [3]
Design of BookingCategory Class & Hierarchy [5]
Design of Passenger Class & Hierarchy [5]
Design of Booking Class & Hierarchy [8]
Design of Exceptions Class & Hierarchy [3]
9.2 Assignment 5: Test Plan, Implementation & Test Report
Implementation [40]
Breakup
Happy Paths [25]
Exceptional Paths [15]
Test Planning [30]
Breakup
Unit Test Scenarios [10]
Application Test Scenarios [5]
Test Cases & Goldens [15]
Testing & Test Report [10]
Breakup
Unit Test Report [7]
Application Test Report [3]
Quality of Design & Implementation [20]
Breakup
Adherence to Design Protocols
Singletons [2] const-ness [2] Sub-Typing [6]
Coding Guidelines [5]
Code Comments [5]
A Coding Guidelines
It is advised to follow the guidelines below while coding:
• Use CamelCase for naming variables, classes, types and functions
• Every name should be indicative of its semantics
• Start every variable with a lower case letter
• Start every function and class with an upper case letter
• Use a trailing underscore ( ) for every non-static data member
• Use a leading ’s’ for every static data member
• Do not use any global variable or function (except main(), and friends)
• No constant value should be written within the code - should be put in the application as static
• Prefer to pass parameters by value for build-in type and by const reference for UDT
• Every polymorphic hierarchy must provide a virtual destructor in the base class
• *Constructors and destructors should never throw
• *Virtual functions should not be called in constructors of base classes
• Prefer C++ style casting (like static cast<int>(x) over C Style casting (like (int))
• Indent code properly
• Comment the code liberally and meaningfully
• Adopt more guidelines as you prefer. Try to document them
B Clarifications
B.1 Queries
B.1.1 Deep Majumder
I have some doubts regarding the new Assignment.
1. It has been mentioned in the assignment that BookingClass can be reduced to a flat hierarchy. But what is the necessity of an explicit hierarchy at all? Combining anonymous namespaces and Factory patterns gives us a way to have Singletons for each booking class. Moreover, this falls in nicely with a Singleton Config manager, which contains master data read from a file. By not having a explicit (flat) hierarchy, we can get rid of a lot of code, possibly even duplicated ones. And also relieves us of explicitly initializing a lot of static constant members (7 * 8 = 56 in for Booking Classes). So is this an acceptable way to model BookingClass? Or is the hierarchy necessary?
Further, I wanted people to first master writing templates, and on hierarchy, without using other existing solution. Without a lot of discussions, it would not be easy for most to handle the solution in the way you are suggesting. However, you are free to use any style you prefer.
2. It has been said that the master data can be read from input files and need not be hardcoded. I plan to use some structured format like YAML, or JSON, or XML. Do I need to provide a schema as well or can I implicitly assume the data format?
3. Reading master data from a file I think introduces a problem with Singletons. In C++, all static member initialization is done before main is executed. As a result, the config file location cannot be passed from main (command line args or otherwise). So it must be hardcoded. But since C++ doesn’t guarantee the order in which static variables are initialized, the filename cannot be stored in a string (or even C-string), because we do not know whether it is initialized or uninitialized (we will have an unreliable design). So the filename must be hardcoded as a string literal. To avoid repeating we have to use a macro (red-flags, I know). Is there a better way out?
PPD: Very interesting question and observation. You have rightly pointed out a tricky situation in terms of global static objects and their initialization (one of the reasons I prefer local static objects whenever possible).
The problem of passing the file name can be addressed if we assume to read it from the stdin which can work even before main() starts (don’t ask how stdin gets initialized and when). This reading of the file name must happen before the first initialization data is needed (and before main() starts). That can be done (check Approach 2 below).
In fact, besides the input file name, there is a deeper problem. The file is a serial structure. It will contain the initialization values in a certain order. And the global static values will be initialized in an unknown order, requiring values coming from the input file. How do we guarantee their alignment?
Here, I shall present three approaches - based on the following three philosophy:
• Approach 1: Do not initialize. Set to default. Set values after main starts.
• Approach 2: Have a singleton to collect all values from input file (this can be done before the first initialization). Then the accumulated values are set for initialization in whatever order they happen.
• Approach 3: Do not use global static data member. Use only local static data with static methods. Think, as if, every static data member is a singleton.
Of course, there could be more. And none of them is perfect. Let me now explain.
Approach 1: The singletons in the project can use the Meyer’s version where they would be local static objects and hence will be constructed only on first use (naturally after main() starts), not before main(). So we do not need to be concerned about them.
Also note that this approach will not work if the static data member is a UDT and does not have a default constructor.
Approach 2: If you abhor the rampant use of friend (I do), we can follow a different scheme. We can have a singleton SetStatic class which reads the static values from the input file during its construction and puts in its data members. So all static initialization will get the value through this singleton object which actually reads the data from the input file. This solves the problem that static data can be initialized in arbitrary order. No matter which order it happens, the first access to static will create this singleton and read the file. A sample code files is given below.
There are four files:
• MyClass.h: This has an abstract base class MyClass with two sub-classes MyClass::MyType1 and MyClass::MyType2 in the emulation of a minimal inclusion-parametric polymorphism (that we are widely using in the design). Each sub-type has four static data members of int, double, string and bool types to show how to set their initial values. This is for the purpose of illustration.
• MyClass.cpp: This file defines the static data members of both sub-types. There is a commented code where these are initialized directly. In the other part they are emulated to have been read from the input file using the SetStatics class.
• SetStatics.h: This is singleton class which is designed with data members as proxy of the static data members of each sub-type above. These are named explicitly for identification without class scopes (this is not good, but works - think about a better solution). The data members are non-const as they have to be set from reading the file. They are made private and endowed with corresponding Get methods (this actually is redundant as these values would not be used after the initialization - still following the usual OOP paradigm). Note that actual reading from file is not shown for simplicity.
• App.cpp: This illustrates the use of the sub-type objects with dynamic dispatch.
// MyClass.h
#ifndef __MY_CLASS_H
#define __MY_CLASS_H
// ***** MyClass class & hierarchy definition
// ***** Author: P P Das
// ***** Version: 1.0
// ***** Known bugs: None
// ***** C++ Standard Library Headers
#include <iostream> #include <string> using namespace std;
// Forward declaration of templatized class template<class T> class MyClassType;
// Generic BookingCategory type class MyClass { // Abstract Base Class
// Tag types struct Type1 { }; struct Type2 { };
protected: MyClass() { } virtual ~MyClass() = 0;
public: virtual void Print() const = 0;
// Enumerated types typedef MyClassType<Type1> MyType1; typedef MyClassType<Type2> MyType2;
}; inline MyClass::~MyClass() {}
// Specific MyClass types template<class T> class MyClassType : public MyClass {
static const string sName; // Name of the person
static const int sAge; // Age of the person
static const double sSalary; // Salary of the person in Rs. Lakhs
static const bool sIsMale; // Gender of the person
MyClassType() : MyClass() { }
~MyClassType() { } public:
// Singleton object - placeholder for the respective type static const MyClassType& Type() {
static MyClassType theObject;
return theObject;
}
void Print() const;
};
// Print methods inline void MyClass::MyType1::Print() const { cout << "Printing a MyType1 Object" << endl; cout << "Name = " << sName << endl; cout << "Age = " << sAge << " years" << endl; cout << "Salary = Rs. " << sSalary << " lakhs" << endl; cout << "Gender = " << ((sIsMale)? "Male": "Female") << endl;
return;
}
inline void MyClass::MyType2::Print() const { cout << "Printing a MyType2 Object" << endl; cout << "Name = " << sName << endl; cout << "Age = " << sAge << " years" << endl; cout << "Salary = Rs. " << sSalary << " lakhs" << endl; cout << "Gender = " << ((sIsMale) ? "Male" : "Female") << endl;
return;
}
#endif // __MY_CLASS_H
// MyClass.cpp
// ***** MyClass class & hierarchy definition
// ***** Author: P P Das
// ***** Version: 1.0
// ***** Known bugs: None
// ***** C++ Standard Library Headers
#include <iostream> #include <string> using namespace std;
// ***** Project Headers
#include "SetStatics.h"
#include "MyClass.h"
// Model for reading from a file through a singleton
const string MyClass::MyType1::sName = SetStatics::Static().GetMyClass_MyType1_sName(); const int MyClass::MyType1::sAge = SetStatics::Static().GetMyClass_MyType1_sAge(); const double MyClass::MyType1::sSalary = SetStatics::Static().GetMyClass_MyType1_sSalary(); const bool MyClass::MyType1::sIsMale = SetStatics::Static().GetMyClass_MyType1_sIsMale();
const string MyClass::MyType2::sName = SetStatics::Static().GetMyClass_MyType2_sName(); const int MyClass::MyType2::sAge = SetStatics::Static().GetMyClass_MyType2_sAge(); const double MyClass::MyType2::sSalary = SetStatics::Static().GetMyClass_MyType2_sSalary(); const bool MyClass::MyType2::sIsMale = SetStatics::Static().GetMyClass_MyType2_sIsMale();
// Setting static values directly
//const string MyClass::MyType1::sName = "Ravi Narayan";
//const int MyClass::MyType1::sAge = 40;
//const double MyClass::MyType1::sSalary = 10.75;
//const bool MyClass::MyType1::sIsMale = true;
//
//const string MyClass::MyType2::sName = "Pratibha Kannan";
//const int MyClass::MyType2::sAge = 37;
//const double MyClass::MyType2::sSalary = 15.30;
//const bool MyClass::MyType2::sIsMale = false;
// SetStatics.h
#ifndef __SET_STATICS_H
#define __SET_STATICS_H
// ***** SetStatics class
// ***** Author: P P Das
// ***** Version: 1.0
// ***** Known bugs: None
// ***** C++ Standard Library Headers
#include <string> using namespace std;
// ***** Project Headers #include "MyClass.h"
class SetStatics {
// Proxy data members for static values string MyClass_MyType1_sName; int MyClass_MyType1_sAge; double MyClass_MyType1_sSalary; bool MyClass_MyType1_sIsMale;
string MyClass_MyType2_sName; int MyClass_MyType2_sAge; double MyClass_MyType2_sSalary; bool MyClass_MyType2_sIsMale;
SetStatics() {
// Read the input file name from stdin - not shown
// Open the input file - not shown
// These values are read from the input file
// This happens only once
MyClass_MyType1_sName = "Ravi Narayan";
MyClass_MyType1_sAge = 40;
MyClass_MyType1_sSalary = 10.75;
MyClass_MyType1_sIsMale = true;
MyClass_MyType2_sName = "Pratibha Kannan";
MyClass_MyType2_sAge = 37;
MyClass_MyType2_sSalary = 15.30;
MyClass_MyType2_sIsMale = false;
}
public:
static const SetStatics& Static() { static SetStatics theObject;
return theObject;
}
// Get methods for the static values we need to set const string& GetMyClass_MyType1_sName() const { return MyClass_MyType1_sName; } const int GetMyClass_MyType1_sAge() const { return MyClass_MyType1_sAge; } const double GetMyClass_MyType1_sSalary() const { return MyClass_MyType1_sSalary; } const bool GetMyClass_MyType1_sIsMale() const { return MyClass_MyType1_sIsMale; }
const string& GetMyClass_MyType2_sName() const { return MyClass_MyType2_sName; } const int GetMyClass_MyType2_sAge() const { return MyClass_MyType2_sAge; } const double GetMyClass_MyType2_sSalary() const { return MyClass_MyType2_sSalary; } const bool GetMyClass_MyType2_sIsMale() const { return MyClass_MyType2_sIsMale; }
};
#endif // __SET_STATICS_H
// App.cpp
// ***** MyClass Application
// ***** Author: P P Das
// ***** Version: 1.0
// ***** Known bugs: None
// ***** C++ Standard Library Headers
#include <iostream> #include <string> using namespace std;
// ***** Project Headers #include "MyClass.h"
int main() { const MyClass& r1 = MyClass::MyType1::Type(); const MyClass& r2 = MyClass::MyType2::Type();
cout << endl; r1.Print();
cout << endl; r2.Print();
return 0;
}
Now the four files will be as follows:
• MyClass.h: Changes static data members from global objects to static methods with local static data. This is given below.
• MyClass.cpp: Definitions of static data members are omitted. This is given below.
• SetStatics.h: Not needed.
• App.cpp: No change except excluding SetStatics.h from inclusion.
// MyClass.h
#ifndef __MY_CLASS_H
#define __MY_CLASS_H
// ***** MyClass class & hierarchy definition
// ***** Author: P P Das
// ***** Version: 1.0
// ***** Known bugs: None
// ***** C++ Standard Library Headers
#include <iostream> #include <string> using namespace std;
// Forward declaration of templatized class template<class T> class MyClassType;
// Generic BookingCategory type class MyClass { // Abstract Base Class
// Tag types struct Type1 { }; struct Type2 { };
protected: MyClass() { } virtual ~MyClass() = 0;
public: virtual void Print() const = 0;
// Enumerated types typedef MyClassType<Type1> MyType1; typedef MyClassType<Type2> MyType2;
}; inline MyClass::~MyClass() {}
// Specific MyClass types template<class T>
class MyClassType : public MyClass {
MyClassType() : MyClass() { }
~MyClassType() { } public:
// Singleton object - placeholder for the respective type static const MyClassType& Type() { static MyClassType theObject;
return theObject; }
// Name of the person
static const string& GetName();
// Age of the person static const int GetAge();
// Salary of the person in Rs. Lakhs static const double GetSalary();
// Gender of the person static const bool IsMale();
void Print() const;
};
// Name of the person inline const string& MyClass::MyType1::GetName() { static const string sName = "Ravi Narayan"; // Read from file
return sName;
}
// Age of the person inline const int MyClass::MyType1::GetAge() { static const int sAge = 40; // Read from file
return sAge;
}
// Salary of the person in Rs. Lakhs inline const double MyClass::MyType1::GetSalary() { static const double sSalary = 10.75; // Read from file
return sSalary;
}
// Gender of the person inline const bool MyClass::MyType1::IsMale() { static const bool sIsMale = true; // Read from file
return sIsMale;
}
// Print methods inline void MyClass::MyType1::Print() const { cout << "Printing a MyType1 Object" << endl; cout << "Name = " << GetName() << endl; cout << "Age = " << GetAge() << " years" << endl; cout << "Salary = Rs. " << GetSalary() << " lakhs" << endl; cout << "Gender = " << ((IsMale())? "Male": "Female") << endl;
return;
}
// Name of the person inline const string& MyClass::MyType2::GetName() { static const string sName = "Pratibha Kannan"; // Read from file
return sName;
}
// Age of the person
inline const int MyClass::MyType2::GetAge() { static const int sAge = 37; // Read from file
return sAge;
}
// Salary of the person in Rs. Lakhs inline const double MyClass::MyType2::GetSalary() { static const double sSalary = 15.30; // Read from file
return sSalary;
}
// Gender of the person inline const bool MyClass::MyType2::IsMale() { static const bool sIsMale = false; // Read from file
return sIsMale;
}
inline void MyClass::MyType2::Print() const { cout << "Printing a MyType2 Object" << endl; cout << "Name = " << GetName() << endl; cout << "Age = " << GetAge() << " years" << endl; cout << "Salary = Rs. " << GetSalary() << " lakhs" << endl; cout << "Gender = " << ((IsMale()) ? "Male" : "Female") << endl;
return;
}
#endif // __MY_CLASS_H
// MyClass.cpp
// ***** Project Headers #include "MyClass.h"
So to conclude Approach 2 seems to be the best option till we find a better solution. It is a bit of coding but is clean and less error-prone. However, I am still concerned with the fact that nice scoped names like
MyClass::MyType1::sName have to be encoded in terms of synthetic names like MyClass MyType1 sName and GetMyClass MyType1 sName() - leaving a huge possibility of manual error. Let us keep looking for a better solution.
4. Since using double-dispatch for object construction (the ”virtual” constructor idiom) tightly couples classes, aren’t we better off simply using the Factory pattern? The double dispatch trick works well with Visitors, but I wonder how useful it is for object construction.
PPD: You are right. I shall try to discuss this more if I get time to talk on various design patterns. For now, it will be too much to expect this from you all without having discussed them in the class.
B.1.2 Kunal Singh
1. Sir in assignment 4 in the use case diagram i am only able to identify passenger as an actor and his only use case being initiation of booking which then includes / extends other dependent use cases could you help me out please ?
2. sir I’ve come up with the following design of booking category actually I got confused with the clarification mail , is this design appropriate ? sorry to bother you again.

B.1.3 Nakul Aggarwal
1. Page No. 22 (highlighted in yellow) (important)

Does this mean that in all the classes where there is a scope of attempting construction with wrongly formatted or invalid inputs, we should make the constructor private and use a static method at its place in the public? (like we do for singleton classes – there we need to preserve the number of calls to the constructor, here we need to preserve the validity of the inputs passed to the constructor)
You would not to do such idioms for constructing objects for classes where no input data validation is necessary, like BookingClass or Concessions. They depend on pre-validated static data only.
2. Relevance of Virtual Construction Idiom in Ad-Hoc Polymorphic Hierarchy Sir, the Concessions class that is rooted at the BookingCategory class realises ad-hoc polymorphism. In this case, how can it perform dynamic dispatch that is required in the ”virtual construction”? Secondly, I am confused with the proposed model of BookingCategory hierarchy. For Concessions hierarchy ad-hoc polymorphism is used. While for Divyaang and PriorityCategories hiearchies, inclusion-parametric polymorphism is used. Both the hierarchies are rooted at BookingCategory class (that might be abstract). Does this mean that among some of the derived classes we are allowing dynamic dispatch and among others we are not? Why can’t we use inclusion polymorphism at the place of ad-hoc? Will virtual construction idiom work with such a ”half ad-hoc half inclusion-parametric hierarchy”?
PPD: You are getting confused between three things - parametric polymorphism, inclusion polymorphism and virtual construction idiom. Let us look at them one by one.
Second, let us see when parametric polymorphism is useful. Using templates, we write a generic code, that instantiates to a number of specific codes based on the type. So the methods of these instantiated classes need to be “parameterizable” - by the values they use and the types they engage. Simply widely different algortihms for different overloads (overrides) of a method would not be a good candidate for parametric polymorphism. Rather, we should use inclusion polymorphism and code every algorithm for every class separately. This is what Concessions warrant because in some cases we do not give concession at all, in some we depend on gender or gender & age, and in others we use the disability information. They are not parametrically combinable. Typically, when we have a flat one level hierarchy, we can use parametric polymorphism for the leaf classes and an abstract base class to provide a uniform interface with dynamic dispatch. That is the case for many class hierarchies here.
Finally, virtual construction becomes necessary when we the particular type of object that we have to construct for a hierarchy (PoolSlot in Section 3.2.2) depends on the type of another object from a different hierarchy (Gender). In our specific context, Booking would be a hierarchy because the fare computation logic depends on the BookingCategory. How do we create an appropriate Booking object then given a specific BookingCategory (and BookingClass)? I hope this clarifies.
3. UML Diagrams Is it totally upto us to decide the level of abstraction of the diagrams? We have seen many class diagrams in the class that have no attributes/operations written in them; only generalization, aggregation etc relationships are used to design these diagrams. So is it fine if we omit some attributes/operations? I am asking this because here we have a lot of classes; this might clutter the diagram a lot if attributes and operations are written for each one of them.
PPD: Of course, it is your choice. However, it is necessary to chose appropriate abstraction (not only limited to properties and methods, there are associations, relationships, message for Sequence etc.) so that all design considerations and details and available “only” from the diagrams. The class diagram in the solution of Assignment 3 could serve as a sample.
B.1.4 Parth Jindal
PPD: You are right. The passenger chooses the Gender from a drop-down (like she / he does for BookingClass or BookingCategory). That process can be emulated by our system by using appropriate Gender or other types in the request. Naturally, these inputs do not need validation - in a GUI system no invalid input can be given for these, and in our system the code will not compile if we provide a wrong type. So, for example, we cannot allow to input a string like “male” for Gender because it is always possible to misspell it as “meal” and the compiler will not give an error (but our runtime system will fail). Hence, it is important these as type constant as explained above.
2. Another question I had in mind was the role of disabilityID in determining the eligibility for Divyaang BookingCategory booking and its validation?
PPD: disabilityID does not need validation because it can come from various agencies and is not regulated to be in a certain format (like aadhaar is). It is more a representative for a certificate that the passenger would need to upload for a GUI based system.
The type of Divyaang is assumed to be from a drop-down in a GUI and will be emulated by type constant so that it cannot be wrong. The BookingCategory details will be validated against it and the fare will be computed by the corresponding business logic. So, Divyaang category of booking can be allowed for Divyaang type passenger only (and the fare will be based on the type of disability and the BookingClass), while General or other category of booking will be allowed for a Divyaang passenger if she / he has sought for it and qualifies.
B.1.5 Rohan Raj
1. In passenger data type, there are many optional attributes. Creating different functions for all of the cases would be time consuming and not that much important. I have an alternative. If A person don’t have a first name, we can pass empty string as the argument. Same goes for all the optional arguments. Can we do that?
PPD: It would be a design choice for you.
B.1.6 Shrinivas Khiste
1. I am having trouble understanding how to implement ad-hoc polymorphism. On the internet, it says that it involves function overloading. Then how is it defined for a class and have a hierarchy? If we use the function overloading definition then we can define different functions to calculate concessions for each type. But how do we implement it for the Exception Classes?
While ad-hoc polymorphism is possible on an inheritance hierarchy, most often it is not interesting and / or useful. What we need there is inclusion polymorphism or function overriding where a member function of a class is redefined with a different behavior from its parent class. This gets useful specially when the inheritance is truly polymorphic (that is, uses pure or non-pure virtual functions). This has also been discussed in depth in the class. You would recall how we used inclusion polymorphism for the draw() method over a hierarchy of shapes. You could use something similar for computing concessions and / or fare in different cases.
Exception classes would usually use static hierarchy because the catch clauses catch the exception by explicit type matching with hierarchical generalization. So using static overriding is the way to go.
B.1.7 Soumita Hait
1. Should constructors and destructor be included in the class diagram?
PPD: It is optional, because it is mandatory for all classes.
2. Are the concession factors fixed or they can vary with time?
PPD: They can change with time.
3. For the Master Data, it is given in the assignment that ”These should be hard-code inside the implementation of functions / methods.” I cannot understand how to hard-code inside functions. Does it mean that I need to create static functions for setting/initializing the values of the various parameters?
PPD: They should not be. It is a typo.
4. It is mentioned in the assignment that ”If there are more than one validation failures, the system should attempt to report as many of them as possible in a single run.” Sir, if an exception arises, it is thrown and detected by the corresponding catch block, after which the program is terminated. Then, how to detect more than one error in a single run? It is also given that we need to classify the exceptions using a hierarchy of Exceptions classes.
That exceptions have a hierarchy, they are layered, are for advantages of deciding which kind of exception to catch where. Like the hierarchy of exceptions, the catch clauses should also be layered on the flow.
Exceptional design is not an easy task. It is good to think about handling such issues. Of course, as a user, if there are three independent errors in the input, you would not like to run the software thrice to get them. You would like to get them all together, fix and then go ahead. We need to design keeping that in mind.
B.1.8 Suhas Jain
1. In section 1.3 Business Logic it is written that the tatkal charges are calculated on the base fare and then the load factor is multiplied to it. But in example 1.3.4 in the calculation, the tatkal charge is calculated after the base fare has been multiplied with the load factor. Which one should we follow?
PPD: Follow the illustrative computations as shown in Sections 1.3.1, 1.3.2, 1.3.3, and 1.3.4.
2. In the Concessions class when we talk about a flat single level ad-hoc polymorphism, how are we supposed to design this? is it like we make a Divyaang class inherit from Concessions or we make separate classes for DivyaangBlind, DivyaangCancer ...etc.?
PPD: You can decide how you would design it. It is a matter of choice. I would rather perceive Concession and Divyaang as separate hierarchies because they are different concepts.
Of course, Concession class would need a kind of DivyaangConcession subclass where BookingClass and Divyaang information is mapped to the concession percentage.
3. In the example of designing gender class by parametric polymorphism, why can’t we model name of the gender just like we did with salutation, why are we making a separate name attribute in the gender base class?
PPD: You can. The name in the gender class is the name of the gender. Salutation can be mapped from this in the output handler. After all, we use male & female to talk about gender and Mr. & Ms. for salutation of the person. They are different concepts.
B.1.9 Yashica Patodia
1. I have a doubt if multiple booking categories are allowed for the same passenger?Like if a senior citizen can avail tatkal benefits and similar multiple other intersections
PPD: No. Not in the same booking. Only one category has to be chosen for a ticket. So it is either senior citizen or tatkal.
Of course, the same person can do different tickets in different categories.