Introduction to Aspect Oriented Programming with Cirrus and Delphi Prism

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Introduction toAspect Oriented Programming with
Cirrus and Delphi Prism

• Jim McKeeth Podcast at Delphi.org

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Agenda

• What is AOP?
• Why AOP?
• Two AOP Paradigms
• The Cirrus Framework
• Examples
• Debugging
• Other AOP Frameworks
• Future

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What is Aspect-OrientedProgramming?
?
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A Paradigm Shift

• Aspect-Oriented programming is to
  Object-Oriented programming

Object-Oriented programming is to Procedural
programming
as
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A Definition

• A programming paradigm that increases modularity
  by enabling improved separation of concerns. This
  entails breaking down a program into distinct
  parts allowing the separation of cross-cutting
  concerns.

Think of it as Super-Encapsulation
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Think of it as Super-Encapsulation
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What is a Concern?

• A distinct and cohesive area of functionality
• Examples
• Business logic
• User interface
• Database access
• Error handling
• Logging
• Threading
• Transactions
• Security
• Exception handling

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What Makes a Concern Cross-Cut?
?
Error handling
Business logic
Thread locking
User Interface
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The Principles of OOD

• SRP The Single Responsibility Principle - A class
  should have one, and only one, reason to change.
• OCP The Open Closed Principle You should be able
  to extend a classes behavior, without modifying
  it.
• LSP The Liskov Substitution Principle Derived
  classes must be substitutable for their base
  classes.
• ISP The Interface Segregation Principle Make fine
  grained interfaces that are client specific.
• DIP The Dependency Inversion Principle Depend on
  abstractions, not on concretions.

Robert C. Martin Uncle Bob www.objectmentor.com
butUncleBob.com
http//butUncleBob.com/ArticleS.UncleBob.Principle
sOfOod
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Two AOP Paradigms

• Pre-Compile / At-Compile
• Decorating the code with the aspects before
  compilation (method used by Cirrus)
• Concerns are woven in during compilation.
• Post-Compile
• Weave the advice in after compilation via
  Point-Cut definitions (method used by AspectJ)
• Allows modification of existing functionality
  without modifying code.

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(No Transcript)
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Bank Transfer
method TBank.Transfer(fromAccount, toAccount
TAccount amount Integer) begin if
fromAccount.Balance lt amount then begin
raise new EInsufficientFundsException() end
fromAccount.withdraw(amount)
toAccount.deposit(amount) end
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With Security
With Security
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With Logging . . . .
With Threading
With Transactions
With ???
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With Cirrus AOP
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Cirrus Fundamentals

• Add reference to RemObjects.Oxygene.Cirrus.
• Not necessary to deploy.
• Aspects must be in a separate assembly.
• Also not necessary to deploy.
• Aspects woven in at compile time.
• Cirrus exists as a series of Interfaces
  (callbacks).
• Aspects are applied via Attributes with the
  aspect prefix.

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• Demo Time

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More on Cirrus

• Cirrus Overview
• prismwiki.codegear.com/en/Cirrus_Overview
• Common Aspect Library
• http//code.remobjects.com/p/prismaspects/
• RemObjects Blog
• Blogs.RemObjects.com/blogs/
• My Blogs
• Delphi.org
• DavinciUnltd.com

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Other AOP Frameworks

• For Delphi Win32
• MeAOP in MeSDK
• code.google.com/p/meaop/
• Other .NET options
• PostSharp.org
• SpringFramework.net
• C
• AspectC.org
• Java
• eclipse.org/AspectJ

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The Futureof AOP
?
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Contact Me

• Jim McKeeth
• jim_at_mckeeth.org
• Twitter.com/JimMcKeeth
• FriendFeed.com/JimMcKeeth
• Delphi.org
• DavinciUnltd.com/Code/Cirrus/ ? Get the slides