Why use aspect-oriented programming

Aspect-oriented programming (AOP) is a programming style that allows you to more easily manage the cross-cutting concerns in your application, meaning those concerns such as authentication or logging that cut across many parts of the app. In essence, AOP is a programming paradigm that enables you to avoid duplicating code and to keep your application easily adaptable to changes.

By taking advantage of AOP, you can increase the modularity of your application through the separation of concerns, as well as reduce code clutter and improve the readability and maintainability of your code.

It should be noted that AOP does not replace object-oriented programming (OOP) in any way. Rather, it complements OOP by providing you with another way to achieve modularity and to reduce code duplication.

What is an aspect in AOP?

An aspect in aspect-oriented programming may be defined as the modularization of a concern. In OOP, you achieve modularity by taking advantage of classes. In AOP, you achieve modularity by taking advantage of aspects. An aspect might be logging or authentication, for example. In AOP, the goal would be to handle all logging or authentication for your application in one place.

The essence of AOP is encapsulating functionalities that are common while at the same time enabling your application to leverage those functionalities as need be. Such common functionalities or cross-cutting concerns include logging, authentication, notifications, transaction management, exception management, etc. Popular AOP frameworks for .NET and C# include Castle Windsor, Microsoft Unity, Policy Injection Block, and PostSharp.

Key concepts of AOP

When working with AOP, you should be familiar with some of the key concepts of the paradigm. These include the following:

• Aspect: A cross-cutting concern or a reusable module. You can have one or more aspects in an application.
• Introduction: A feature that is used to declare additional methods and attributes for a particular type.
• Join point: A point where you can plug in an aspect.
• Advice: An action that is performed at a particular join point. An advice is also used to define the action that should be performed preceding or succeeding a method execution.
• Weaving: A weaving enables links an aspect with other objects of the application, providing a solution to your tangled code. Note that, depending on where weaving occurs, you can have compile-time, load-time, or run-time weaving.
• Target object: A target object may be defined as one that is advised by one or more aspects in your application.
• Pointcut: A pointcut is used to define the weaving rules and the join point where a particular advice can be applied in your application.

Key benefits of AOP

OOP promotes reusability and flexibility of code already. So, why then do you need AOP? In addition to all the benefits of OOP, AOP promotes loose coupling and enables the use of pluggable aspects when needed without requiring any changes to your application’s code. When using AOP, you can focus on the business logic of your application while at the same time weaving aspects into the business logic. One of the major benefits of using AOP is that you only need to write your aspects once and then you can reuse them wherever you need to in your application. Thus AOP is a great way to reduce the complexity of the source code of your application and keep your code clean and modular.

The key benefits of AOP include:

• Reduced code clutter
• Reduced code redundancy
• Easier code maintenance
• Faster development
• Improved code readability

Implementing AOP in your application

Implementing AOP in your applications is a two-step process. First, you isolate the aspects of your application, i.e. the cross-cutting concerns, from the business logic. The most important thing to keep in mind when designing the aspects is that they should be independent—they should not have any dependencies on the application. You should be able to test the aspects independently of one another as well. Second, you then apply those aspects to the application’s source code by weaving them wherever they are needed by the application.

One of the ways you can implement AOP in C# is by using attributes. Recall that attributes in C# allow you to attach metadata, or additional information, to your classes, methods, and properties. However, you can also use attributes to indicate what actions should be applied to the code at run time.

Consider the following code snippet that illustrates how you can define a custom attribute in C#.

public class LogAspectAttribute : Attribute
{

}

You can then decorate your methods to intercept using the attribute you defined, in this case LogAspectAttribute.

using System;
public class DemoService
{
    [LogAspect]
    public void Display(string data)
    {
        Console.WriteLine(data);
    }
}