SOLID PRINCIPLESby Steven Ndaye

…GROUND RULES…

Solid principles are just bunch of guidelines, not hard and fast rules

In most cases, we will be required to use our brain and do what makes sense to us

We also be required to always ask WHY…

The SOLID principles are principles of object oriented class design.

Object oriented programming is defined as a method programming based on a hierarchy of classes, and well-

defined and cooperating objects.

…WHY DOES IT MATTER?

You code is going to change. Flexibility will be required

Make your code more reusable(DRY)

Testability

Make out lives easier

SOLID PRINCIPLES

Agile Software Development Principles, Patterns and Practices, by Robert C.Martin(aka “Uncle Bob” Martin)

SRP“None but Buddha himself must take the responsibility of giving out occult secrets…”

SPR

Cfr project(SRP example1 and example2) https://github.com/StevenNdaye/solid-principles-session

POSSIBLE SRP CODE SMELLS

Long classes(and methods)

God classes

LONG CLASSES

POSSIBLE SOLUTIONS: LAYERS

UI#

Business'Logic'(Domain'Model)'

Data$Access$

Database'

LONG CLASSES

God classes

POSSIBLE SOLUTIONS: VERBS

Smaller classes and smaller methods will give you more flexibility, and you

don’t have to write much extra code to do it.

SRP matters because we want it to be easy to reuse code since bigger classes are difficult to change and

harder to read.

OCP“Dutch door. Noun. A door divided in two horizontally so that either part can be left open or closed”

Software entities(classes, modules, methods) should be open for extension but closed for modification…

OCP

Cfr project(OCP example1 and example2) https://github.com/StevenNdaye/solid-principles-session

OCP RULE OF THUMB

Use if/switch if the number of cases is unlikely to change

Use strategy pattern when the number of cases are likely to change

LSPSubtypes must be substitutable for their base types.

Meaning that a subclass should behave nicely when used in place of their

base class.

Functions that use pointers or references to base classes must be able to use objects of derived classes

without knowing it…

ISPClients should not be forced to depend on interfaces that they do not use.

DIPNevermore Let the great interests of the State depend Upon the thousand chances that may sway A piece of human frailty.

High level modules should not depend on low level modules. Both should depend on abstractions.

Abstractions should not depend upon details. Details should depend upon abstractions.

POSSIBLE SOLUTIONS: LAYER WITH INTERFACES

UI#

Business'Logic'(Domain'Model)'

Data$Access$

Database'

Interfaces*

Interfaces*

Steven Ndaye

THANK YOU !

For all the examples, please clone this repo @ https://github.com/StevenNdaye/solid-principles-session