Aspect-Oriented Programming with Dependency Injection

Mark Seemann

@ploeh

Cross-Cutting Concerns

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Tran

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Secu

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Objective

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

SOLID

•Don’t Repeat Yourself DRY

Staying SOLID

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

SOLID

•Don’t Repeat Yourself DRY

Prerequisite

Program to an interface, not an implementation

- Design Patterns,

1995

Conjecture

• It’s always possible to apply a Decorator to an interface

Using Decorators to add aspects

IFoo

ConcreteFoo

Client

Using Decorators to add aspects

IFoo

AuditingFoo

IFoo

ConcreteFoo

Client

Using Decorators to add aspects

IFoo

SecureFoo

IFoo

AuditingFoo

IFoo

ConcreteFoo

Client

DEMO

Staying SOLID with Decorators

Staying SOLID

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

SOLID

•Don’t Repeat Yourself DRY

Staying DRY

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

SOLID

•Don’t Repeat Yourself DRY

Dynamic interception

From here on, dynamic interception is required

Commonly supplied by

a DI Container

DI Containers with Interception

Castle Windsor

Unity

Spring.NET LinFu

DEMO

Using a DI Container

Interception

Xyz

Interception

Xyz

IFoo

XyzFoo

Xyz

Interception

Xyz

IFoo

XyzFoo

Xyz

IBar

XyzBar

Xyz

Interception

Xyz

IFoo

XyzFoo

Xyz

IBar

XyzBar

Xyz

IBaz

XyzBaz

Xyz

DEMO

Adding interceptors

Pointcut

Xyz

Abc

Æøå

IFoo

ConcreteFoo

IBar

ConcreteBar

IBaz

ConcreteBaz

Pointcut

Xyz

Abc

Æøå

IFoo

ConcreteFoo

IBar

ConcreteBar

IBaz

ConcreteBaz

Match

DEMO

Adding a pointcut

Objective

•Single Responsibility Principle

•Open/Closed Principle

•Liskov Substitution Principle

•Interface Segregation Principle

•Dependency Inversion Principle

SOLID

•Don’t Repeat Yourself DRY

Staying SOLID only

requires loose

coupling

Staying DRY requires dynamic

interception

MARK SEEMANN

http://blog.ploeh.dk/

@ploeh