The SOLID Principles are the design principles that enable us to manage several software design problems. These principles provide us with ways to move from tightly coupled code to loosely coupled and encapsulated real business needs properly. Also readable, adaptable, and scalable code.
The SOLID Principles guide developers as they write
readable, adaptable, and scalable code or design an application.
The SOLID Principles can be applied to any OOP program.
The SOLID Principles were developed by computer science instructor and author Robert C. Martin. Now, SOLID principles have also been adopted in both agile development and adaptive software development.
The 5 principles of SOLID are:
1. Single Responsibility Principle (SRP)
2. Open-Closed Principle (OCP)
3. Liskov Substitution Principle (LSP)
4. Interface Segregation Principle (ISP)
5. DependencyInversion Principle (DIP)
Open-closed principle (OCP):
The Open/closed Principle says that a software module/class/function is open for extension and closed for modification. That means a class should be easily extended but there is no need to change its core implementations.
“Software entities … should be open for extension, but closed for modification.” Robert C. Martin.
Implementation:
Let’s take an example of bank accounts like regular savings,
salary savings, corporate, etc. for different customers. As for each customer
type, there are different rules and different interest rates.
The below Account class code violates the OCP principle, if the bank
introduces a new Account type in that case, we need to modify CalcInterest
method for adding a new account type.
The code looks like,
// Does not follow a Open-closed
principle (OCP)
public class Account
{
public decimal InterestRate
{ get; set; }
public decimal BalanceAmount { get; set; }
//members and function declaration
public decimal
CalcInterest(string accountType)
{
// saving Account type
if (accountType
== "Regular")
{
InterestRate = (BalanceAmount * 4) / 100;
if
(BalanceAmount < 1000) InterestRate -= (BalanceAmount * 2) / 100;
if
(BalanceAmount < 5000) InterestRate += (BalanceAmount * 4) / 100;
}
// salary Account type
if (accountType
== "Salary")
{
InterestRate
= (BalanceAmount * 5) / 100;
}
// Corporate Account type
if (accountType
== "Corporate")
{
InterestRate
= (BalanceAmount * 3) / 100;
}
return
InterestRate;
}
}
We can apply the Open-closed principle (OCP) by using interface,
abstract class, abstract methods, and virtual methods when we want to extend
functionality.
Here in the below, we have used interface (IAccount) to follow an Open-closed principle (OCP) or remove the code that violates OCP principle,
interface IAccount
{
// members and function declaration, properties
decimal
BalanceAmount { get; set; }
decimal
CalcInterest();
}
//regular savings account
public class RegularSavingAccount : IAccount
{
public decimal
BalanceAmount { get; set; } = 0;
public decimal
CalcInterest()
{
decimal InterestRate
= (BalanceAmount * 4) / 100;
if
(BalanceAmount < 1000) InterestRate -= (BalanceAmount * 2) / 100;
if (BalanceAmount < 5000) InterestRate += (BalanceAmount * 4) / 100;
return
InterestRate;
}
}
//Salary savings account
public class SalarySavingAccount : IAccount
{
public decimal
BalanceAmount { get; set; } = 0;
public decimal
CalcInterest()
{
decimal InterestRate
= (BalanceAmount * 5) / 100;
return
InterestRate;
}
}
//Corporate Account
public class CorporateAccount : IAccount
{
public decimal
BalanceAmount { get; set; } = 0;
public decimal
CalcInterest()
{
decimal InterestRate
= (BalanceAmount * 3) / 100;
return
InterestRate;
}
}
In the above code, three new classes are created by extending them
from IAccount.
1. RegularSavingAccount
2. SalarySavingAccount
3. CorporateAccount
This is solving the problem of modification of class and by
extending the interface, we can extend functionality.
The above code implements both the Open-closed principle (OCP) as well
as the Single-responsibility principle (SRP) principle, as each class does a
single task and we are not modifying the class and only doing an extension.
Use Cases of Open-Closed Principle in C#:
The Open-Closed Principle (OCP) is one of the SOLID principles of object-oriented programming, and it states that a class should be open for extension but closed for modification. In C#, there are several ways to apply the Open-Closed Principle to improve the flexibility and maintainability of your code.
Here are some use cases:
1. Adding new
functionality through inheritance
2. Using
interfaces for extension
3. Using
strategy pattern
4. Using
Abstract Factories
5. Using
Dependency Injection
By applying the Open-Closed Principle in these ways, you can
enhance the flexibility of your code, make it easier to extend, and reduce the
risk of introducing bugs when adding new features.
Advantages of Open-Closed Principle:
1. Code
Reusability
2. Maintainability
3. Reduced
Risk of Regression Bugs
4. Encourages
Design Patterns
5. Scalability
Disadvantages of Open-Closed Principle:
1. Performance
Impact: added extra layers might decrease performance due to added indirection
2. Abstraction
Overhead: added unnecessary abstraction overhead