Single Level of Abstraction (SLA) Principle

The Single Level of Abstraction principle asserts that a function or method should operate at a single level of abstraction. This means that within a given function, all statements should be at the same conceptual level, avoiding the mix of high-level and low-level operations.

In software design, some principles get a lot of attention, while others are just as important but less well-known. One of these lesser-known but very useful principles is the Single Level of Abstraction (SLA). Following SLA can make your code easier to read, understand, and maintain.

Why is SLA Important?

1. Easier to Read: When a function sticks to one level of detail, it's easier to understand. You can quickly see what the function is supposed to do.
2. Easier to Maintain: Keeping functions focused and consistent makes it easier to change or fix things later. You won't have to untangle mixed levels of detail.
3. Easier to Debug: When functions follow SLA, it's simpler to find and fix problems. High-level functions handle overall control, and low-level functions handle specific tasks.

Examples of SLA

Let's look at an example in C# to see how SLA works.

Violating SLA

Here's a method that mixes different levels of detail:

public void ProcessOrder(Order order)
{
    // High-level task: Orchestrating order processing
    ValidateOrder(order);
    
    // Low-level task: Saving order to the database
    using (var connection = new SqlConnection(connectionString))
    {
        connection.Open();
        var command = connection.CreateCommand();
        command.CommandText = "INSERT INTO Orders VALUES (...)";
        command.ExecuteNonQuery();
    }
    
    // High-level task: Sending confirmation email
    SendConfirmationEmail(order);
}
        

In this example, ProcessOrder mixes high-level tasks (like validating the order and sending an email) with low-level details (like saving to the database). This makes it harder to read and maintain.

Adhering to SLA

Now, let's refactor the method to follow SLA:

public void ProcessOrder(Order order)
{
    ValidateOrder(order);
    SaveOrderToDatabase(order);
    SendConfirmationEmail(order);
}

private void SaveOrderToDatabase(Order order)
{
    using (var connection = new SqlConnection(connectionString))
    {
        connection.Open();
        var command = connection.CreateCommand();
        command.CommandText = "INSERT INTO Orders VALUES (...)";
        command.ExecuteNonQuery();
    }
}
        

Now, ProcessOrder is a high-level function that orchestrates the order processing steps and SaveOrderToDatabase is a low-level function that handles the details of saving the order. Each function is focused and easier to understand.

How to Apply SLA in Real-Life

1. Spot Mixed Levels: Look at your functions and see if they mix high-level and low-level tasks. If they do, split them into separate functions.
2. Delegate Tasks: High-level functions should delegate tasks to low-level functions. This keeps each function focused.
3. Keep Consistent Levels: Make sure your functions across your codebase are consistent in their levels of detail. This makes the whole codebase easier to navigate and understand.

Conclusion

The Single Level of Abstraction (SLA) principle might not be as famous as other principles, but it's very powerful. By making sure each function only handles tasks at the same level of detail, you can make your code easier to read, maintain, and debug.

Start using SLA in your coding practices and see how it improves your development process. By writing clear and focused code, you'll create software that's not just functional but also clean and robust.