View on factory design pattern implementation

Question

Hi All

I have tried implementing factory design pattern as below:
https://code.sololearn.com/c7d7F6P8EWIT

Could you please help me with comment on the same whether is there any improvement can be done or not in above code?

Additionally, I would like to know can we change this code in some way that make it abstract factory pattern? I would like to understand this.

Any view on this would be of great help.

Thanks...!

Answer 1

Nice code Ketan Lalcheta .I'll give you some tips that I consider good for optimal and nearly bug-free code.
1.Make your classes as self-contained as you possibly can(minimise dependencies on global types,functions and objects(unless they belong to the standard library)
In your case,the enum should be a public member of your class and not a global entity

Answer 2

2.Avoid using plain,old,C-style enums.Opt for enum classes to avoid surprises(hard-to-find bugs) mostly brought about by implicit conversion of the enumerators to int and also to improve readability and ultimately, maintainability of your code

Answer 3

4.Don't redeclare methods in derived classes as being virtual(since they are already virtual by default).Instead use the "keyword" override written just before the opening curly bracket {,since this makes it clear and explicit that a particular method overrides another declared in some base class up the hierarchy

Answer 4

5.Lastly and most importantly, try as much as possible(I'm even inclined to use the words absolutely avoid) to not handle memory yourself..Instead,assign the allocated memory to a resouce handler,preferably a unique_ptr
For example.In your case you could write
unique_ptr<clsTravsl> p1{ clsTravel::GetTravelObject(Road)};

Answer 5

3.Avoid defining ordinary functions within the class definition unless you really want the functions inlined by the compiler

Answer 6

Finally,when calling the static getTravelObject method in main, you should fully resolve the enumerators' scope(Two scopes in this case, the enum class scope and class clsTravel scope) like this
unique_ptr<clsTravel> p1{clsTravel::GetTravelObject(clsTravel::enmTransportMode::Road)};

Answer 7

This is how I would define the base class
class clsTravel
{
public:
enum class enmTransportMode{ Road , Rail , Air };
clsTravel()=default;
virtual ~clsTravel()=0;
virtual void display()=0;
static clsTravel* GetTravelObject(enmTransportMode);
};

Answer 8

Next,modify the static getTravelObject method definition to return a nullptr,since the base class is now abstract and thus you cannot instantiate it

Answer 9

Doing so would not cause issue to provide the same enum to argument of GetTravelObject methods from main function ?

Answer 10

Wow... Something new i learnt... I never thought enum can be accessed by class name (no need to have object) directly without declaring the same as static..

Answer 11

Anthony Maina thank you so so much for this... I have tried and implemented above points in new version of code as below:

https://code.sololearn.com/cDSoZZGFf6Wp

However, I could not take enum inside of class even as public member also. I belive it might not be possible in this case as I had to create object unnecessary for abstract class which is not possible.

Please share your thoughts on this whether this code is fine or abstraction is to be removed ?

Answer 12

Yes it's possible to move the enum class into the abstract base class