DRY Principle
Published: 2023-05-01 07:45:51

The Don't Repeat Yourself (DRY) is:

> _A fundamental software development philosophy emphasizing the importance of avoiding code duplication._

It advocates that every piece of knowledge or logic in the code should have a single, clear, and definitive representation within a system.

## Violation of the principle

Violating the DRY principle means repeating the same logic or information in multiple parts of the code. This practice can lead to significant issues:

- **Difficult maintenance**: Duplication makes the code harder to maintain. If a logic needs to be changed, it has to be changed in every place where it's duplicated.
- **Increased errors**: The presence of duplicated code increases the risk of errors and inconsistencies, as a change in one part may not be replicated in others.
- **Difficult comprehension**: Duplicated code can make the system harder to understand, especially for new developers getting acquainted with the project.

Imagine we have several functions that need to validate an array of data before proceeding with specific calculations. Instead of centralizing the validation logic, the validation code is repeated in each function:

```csharp
public class StatisticsCalculator
{
    public double CalculateMean(int[] data)
    {
        if (data == null || data.Length == 0)
        {
            throw new ArgumentException("Invalid data");
        }

        // Mean calculation
    }

    // Other methods with duplication of validation logic
}
```

## Application of the principle

To apply the DRY principle in code, it is essential to identify parts of the code that are or might be repeated and abstract this logic into a single reusable unit.

Suppose we have several functions that calculate different types of statistics, but all share a common step of data validation. Instead of repeating the validation code in each function, we can abstract it into a separate method.

``` csharp
public class DataValidator
{
    public static bool IsValidData(int[] data)
    {
        return data != null && data.Length > 0;
    }
}

public class StatisticsCalculator
{
    public double CalculateMean(int[] data)
    {
        if (!DataValidator.IsValidData(data))
        {
            throw new ArgumentException("Invalid data");
        }

        // Mean calculation
    }

    // Other methods using DataValidator
}
```

## Conclusion

In this article, we have explored the DRY (Don't Repeat Yourself) principle in the context of software development, emphasizing how its application leads to cleaner, more manageable, and less error-prone code. We saw an example of violating the DRY principle, where the repetition of validation logic in various methods leads to difficulties in maintenance and code updating. In contrast, abstracting such logic into a separate method demonstrates an effective application of the DRY principle. Adhering to this principle is crucial for efficient and easily maintainable software development, but it is important to maintain a balance, avoiding excessive abstraction that could unnecessarily complicate the code. Ultimately, the goal is to create code that is not only efficient but also clear and simple to understand.

## References

- [The Pragmatic Programmer, 20th Anniversary Edition](https://pragprog.com/titles/tpp20/the-pragmatic-programmer-20th-anniversary-edition/)