Polyglot Poly Paradigm

8/13/2019 Polyglot Poly Paradigm

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Polyglot and

Poly-paradigmProgramming

Dean [email protected]

@deanwampler

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Monday, June 14, 2010
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Co-author,Programming

Scala

programmingscala.com



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Todays

applications:

Are networked,

Have graphicaland serviceinterfaces,

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Todays

applications:

Persistdata,Must be resilient

andsecure,

Must scale,7



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Todays

applications:

and must doall that by Friday.

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Polyglot or

Multilingual:

many languages

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Poly-paradigmor

Multiparadigm:many modularity

paradigms

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Thesis:

modern problemsare poorly served by

Monocultures

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monocultures => monoglot and mono-paradigm programming.


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Mono-

paradigm:

Object-OrientedProgramming:

right for allrequirements?

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Is one language

best for all domains?

Monolingual

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domains: e.g., the problem domain for the app (usually an object model), the security model, the network/web topology, therelational or other data model, ...


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Symptomsof

Monocultures

Why is there so muchXMLin myJava? Why do I have similar code for persistence,

transactions,security,etc. scattered all over my

code base?

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Symptomsof

Monocultures

How can I scalemy application to internet scales? Why is my application so hard to extend?

Why cant I respondquickly when requirements

change?

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Pervasive Symptom:

Toomuch

code!16



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Lets examine some

common problems

withPPPsolutions:

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Change

is slowand painful.

Problem #1

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Symptoms

Featurestake toolongtoimplement.

We cant reactfast enoughto change.

Uses want to customizethe

system themselves.19Monday, June 14, 2010


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Solution

Application

Kernelof Components

User Scripts Built-in Scripts

(C Components) + (Lisp scripts) = Emacs

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Components+ Scripts

=Applications

see John Ousterhout, IEEE Computer, March 98

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Pronunciation: OH-stir-howt


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Kernel Components

Statically-typed language:

C, C++, Java, C#, ...

Compiledfor speed, efficiency.

Access OS services, 3rd

-partylibraries.

Lower developer productivity.22Monday, June 14, 2010


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Scripts

Dynamically-typed language:

Ruby, Lisp, JavaScript, Lua, ...

Interpretedfor agility.

Performanceless important.

Gluetogether components.

Raise developer productivity.23Monday, June 14, 2010In practice, the divide between components and scripts is not so distinct.


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In practice,

the boundariesbetweencomponentsand scripts

are not so distinct...

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Other Examples:

UNIX/Linux+ shells.Also find, make,grep, ...

Have their own DSLs.

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C++/Lua Examples:

Adobe Lightroom 40-50% written in Lua.

Game Engines

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Lightroom: Lua API used for 3rd-party plugins.Lots of games combine C++ and Lua, too.


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Embedded Systems:

Tektronix Oscilloscopes: C +

Smalltalk. NRAO Telescopes: C + Python.

Google Android: Linux +libraries (C) + Java.

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Oth E l


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Other Examples:

Multilingual VMs

On theJVM: JRuby, Groovy, Jython,

Scala. Ruby on Rails on JRuby.

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Another realization of C+S=A is to put several languages on the same VM, rather than using the OS as the component layer.

Oth E l


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Other Examples:

Multilingual VMs Dynamic Language Runtime

(DLR).

Ruby, Python, ... on

the .NET CLR.

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Another realization of C+S=A is to put several languages on the same VM, rather than using the OS as the component layer.


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XMLin Java

Why not replaceXML

withJavaScript , GroovyorJRuby??

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De facto scripting language in Java.Not an optimal choice:- All data.- No behavior (to speak of...).- Verbose.


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Benefits

Optimizeperformancewhere it matters. Optimize productivity,extensibility, agility and

end-user customization everywhere else.

Application

Kernelof Components


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This is an underutilized architecture.


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Anunderutilizedarchitecture!

Application

Kernelof Components


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Parting Thought...

Why dont Eclipse, IntelliJ, etc.have built-in scriptingengines?

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The intent

of our code

is lostin the noise.37



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Symptoms

New team members have along learning curve.

The system breakswhen wechangeit.

Translating requirementsto codeis errorprone.

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Solution #1

Writeless code!

Youre welcome.

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Less Code

Means problemsare smaller:

Maintenance

Duplication

Testing

Performance

etc. 40Monday, June 14, 2010


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S 2


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Solution #2

Separateimplementationdetails

from businesslogic.

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Domain Specific

LanguagesMake the code read like

structured domain prose.

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Example DSLinternal{ caseextension


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p when100...200

callee=User.find_by_extensionextension

unlesscallee.busy?thendialcallee

else

voicemailextension

when111 thenjoin111

when888playweather_report('Dallas, Texas')

when999

play%w(a-connect-charge-of 22

cents-per-minute will-apply) sleep2.seconds

play'just-kidding-not-upset'

check_voicemail

end

}

Adhearsion=

Ruby DSL+

Asterisk+

Jabber/XMPP+...

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PBX = Private Branch Exchange, the telephony exchange that serves a business or other o!ce, etc.

DSL Ad


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DSL Advantages

Code lookslike domain prose:

Is easier to understand byeveryone,

Is easier to alignwith the

requirements,

Is more succinct.45


DSL Di d


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DSL Disadvantages

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Many people arepoorAPI designers.

DSLs are harderto design.


DSL Di d


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DSL Disadvantages

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DSLs can be hardtoimplement, test, and debug.



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Not too many of this examples yet, but one comes to mind: mocking (for testing) frameworks in Ruby, BDD tools in severallanguages.


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Parting Thought...Perfectionis achieved,

not when there is nothing left to add,but when there is nothing left to remove.

-- Antoine de Saint-Exupery

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He wrote The Little Prince, among other books. He was an aviator who disappeared over the Mediterranean in 1944, flying forFree French Forces.


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Parting Thought #2...

Everything should be made as simpleas possible, but not simpler.

-- Albert Einstein

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Corollary:Entia non sunt multiplicanda

praeter necessitatem.

-- Occams Razor

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a.k.a. Law of Parsimony or Law of Succinctness. Paraphrased translation.


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Corollary:All other things being equal,

the simplestsolutionis the best.

-- Occams Razor

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a.k.a. Law of Parsimony or Law of Succinctness. Paraphrased translation.

We have


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codeduplicationever where.

Problem #3


Symptoms


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Symptoms

Persistence logicis embeddedin everydomain class.

Error handling and logging isinconsistent.

Cross-Cutting Concerns.

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Solution

Aspect-Oriented

Programming

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Removing Duplication


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Removing Duplication

In order, use:

Objector functionaldecomposition.

DSLs.

Aspects.

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Make sure your object and functional decomposition is right first, then use DSLs appropriately. Finally, use aspects.


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classBankAccount


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attr_reader :balance

def credit(amount)

@balance+= amount

end def debit(amount) @balance-= amount

end

end

Clean Code

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But, real applications need:


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But, real applications need:

def BankAccount

attr_reader :balancedef credit(amount)

... end

def debit(amount)...

end

end

Transactions

Persistence

Security

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So creditbecomes


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defcredit(amount) raise if unauthorized()

save_balance = @balance

begin

begin_transaction()

@balance+= amount persist_balance(@balance)

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rescue => error log(error)

@balance= saved_balance

ensure

end_transaction()

endend

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Were mixing multipledomains,


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g p

Transactions

Persistence

Security

with fine-grained intersections.

Problem Domain

tangled code

scattered logic62


In principle, I can reason about transactions, etc. in isolation, but in reality, the code for transactions is scattered over the wholesystem. Similarly, the once-clean domain model code is tangled with code from the other concerns.Objects dont prevent this problem (in most cases).


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Objectsalonedontpreventtangling.

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Aspect-OrientedProgramming:

restore modularityforcross-cutting concerns.

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Aspectsrestore modularityby


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p y y

encapsulating the intersections.Transactions

Persistence

Security

TransactionAspect

PersistenceAspect

SecurityAspect

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See extra slides



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If you have used the

Spring Framework,you have

usedaspects.

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Parting Thought...


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a t g oug t...

Metaprogrammingcan be usedfor some aspect-likefunctionality.

DSLscan solve somecross-cutting concerns, by localizingbehaviors expressed by the DSL.

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Our service


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Problem #4

flickr.com/photos/wolfro54

Our service

must beavailable 24x7

and highlyscalable.


Symptoms


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y p

Only oneof our developers

reallyknowshow to writethread-safecode.

The system freezesevery fewweeksor so.

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Solution

Functional

Programming

70Monday, June 14, 2010

(At least, its one solution...)

Functional Programming


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g g

y = sin(x)

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Modeled after mathematics.




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g g

y = sin(x)

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Values are immutable.Variables are assigned once.




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g g

y = sin(x)

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Functions are side-effect free.Functions dont alter state.

The resultdepends solelyon the arguments.


Functional Programming:


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g g

ConcurrencyIsEasier

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No writes,so no synchronization.Hence, nolocks, semaphores, mutexes...

y = sin(x)


Functional Programming:


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g g

ReasoningisEasier

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Without side effects,functions are easierto test, understand, ...

y = sin(x)

and reuse!


Which fits your needs?


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Object Oriented

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Account

deposit(...)

withdraw(...)

CheckingAccount

deposit(...)

withdraw(...)

SavingsAccount

deposit(...)

withdraw(...)

??

deposit(...)

withdraw(...)


Do operations vary significantly, depending on data type or ...

Which fits your needs?


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list map

fold/

reduce

filter

Functional

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or do operations more or less work the same independent of the data type?

What if


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What ifyoure

doing cloudcomputing?

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E.g., is map-reduceobject-orientedor functional?


FP Code:


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more declarativethan imperative.

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F(n) = F(n-1) + F(n-2)

where: F(0) = 0 and F(1) = 1

0, 1, 1, 2, 3, 5, 8, 13, ...


The Fibonacci Sequence.I tell the system what I want (e.g., what are the relationships between data, the constraints, etc.) and let the system figure outhow to do it.

and so are DSLs.


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classCustomer < ActiveRecord::Base

has_many :accounts

validates_uniqueness_of :name,

:on =>create,

:message=>Evil twin!

end


By hiding the implementation details, we have much more leeway in implementing aspect behavior, etc.


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A FewFunctionalLanguages



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Erlang


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No mutable variablesand side effects.

Uses the actor modelof concurrency.

All IPC is optimized message passing.

Let it fail philosophy.

Verylightweight and fast processes. Lighter than most OS threads.

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Scala


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Hybrid: object and functional.

Targets theJVMand .NET. EndorsedbyJames Goslingat JavaOne.

Could be the most popular

replacementfor Java.

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Times Change...


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...


Clojure


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Functional, with principledsupport formutability.

Targets theJVMand .NET.

Bestbuzz?

Too manygood ideasto name here...

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Functional Languages inIndustry


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Industry

Erlang

CouchDB, Basho Riak, andAmazonsSimple DB.

GitHub

Jabber/XMPP server ejabberd.

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Parting Thought...


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Which is better:A hybrid object-functionallanguage

for everything?An objectlanguage for some code anda functionallanguage for other code?

e.g., Scalavs.Java +Erlang??

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Scala is more complex than mono-paradigm languages, so its harder to master. However, using multiple languages has itsown challenges.


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PolyglotandPoly-paradigmProgramming(PPP)

Recap:

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Disadvantagesof PPP


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Ntool chains, languages, libraries,ecosystems, idioms, ...

Impedance mismatchbetween tools.

Different meta-models.

Overheadof calls between languages.

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Advantagesof PPP


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Can use the best toolfor a particular job.

Can minimize the amountof code

required.

Can keep code closerto the domainusing DSLs.

Encourages thinking about architecture.

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Is This New?


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Functional Programming Comes of Age.

Dr. Dobbs, 1994

Scripting: Higher Level Programming forthe 21stCentury.

IEEE Computer, 1998

In Praise of Scripting: Real ProgrammingPragmatism.

IEEE Computer, 2008Monday, June 14, 2010

Why go mainstreamnow?


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Rapidly increasing pace of development,!Scripting (dynamic languages), DSLs.

Pervasive concurrency(e.g.,Multicore CPUs)!Functional programming.

Cross-cutting concerns

!Aspect-oriented programming.

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Thank You!


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[email protected]

Watch for the IEEE Softwarespecial issue, Sept/Oct 2010. polyglotprogramming.com

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Extra Slides

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I would like to write


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Beforereturning the balance, readthecurrent valuefrom the database.

Beforeaccessing the BankAccount,authenticateandauthorizethe user.

Aftersetting the balance, writethecurrent valueto the database.

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Aftersetting the balance, writethecurrent valueto the database.

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Aquariumuse aquarium lib.


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require aquariumclassBankAccount

after :writing => :balance \ do |context, account, *args|

persist_balanceaccount

end

reopen class

event to trigger on

aquarium.rubyforge.org100

new behavior



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