writing extensible applications

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Writing Extensible Applications

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About meabout me…

Andrey Yatsenco

● PHP Developer at Oro Inc.● 3 years with Symfony ● 6 years with PHP

https://www.facebook.com/yatsencohttps://github.com/anyt

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Writing Extensible Applications

Agenda● Definition● Common solutions● What Symfony offers

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When applications should be extensible?

When you write:● a lot of similar apps● requirements change a lot● a lot of features in one app● open-source

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provide for change (enhancements)● while minimizing impact to existing system

functions.● is a design principle where the

implementation takes future growth into consideration.

● extensions can be through the addition of new functionality or through modification of existing functionality

Extensibility

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Extensible design is to accept that not everything can be designed in advance

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Why code mustbe extensible?

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Typical problems of not extensible apps

● Difficult to replace part of an app● Difficult to scale an application

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Common solutions

● Abstractions and DI● Modular design● Extensions provider● Event-driven architecture

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Common solutions

● Abstractions and DI● Modular design● Extensions provider● Event-driven architecture

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Abstractions and DI

Abstractions: Dependency Injection:

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Common solutions

● Abstractions and DI● Modular design● Extensions provider● Event-driven architecture

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Modular design

Examples:● Symfony● ZF● Yii● Drupal● Joomla● Wordpress● etc.

Naming:● modules● bundles● packages● plugins● service providers● etc.

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Modular design

Make your framework modular:● Symfony HttpKernel component (bundles)

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Modular design

Separating the functionality of a program into independent, interchangeable modules, such that each contains everything necessary to execute only one aspect of the desired functionality.

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Modular design

Bad practices:● High Cohesion● Circular references

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Modular design

Bad practices: How to avoid this?

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Modular design

Bad practices:

How to avoid this?● Event-driven architecture

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Event-driven architecture

● Observer● Mediator

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Event-driven architecture

Observer:

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Event-driven architecture

Mediator

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Modular design

Bad practices:

How to avoid this?● Event-driven architecture● Providing extensions

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Providing extensions

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What Symfony offers?

● Bundles● Service container● Event dispatcher

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What Symfony offers?

Service container● Dependency Injection

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What Symfony offers?

Service container● Overriding classes of services with the

same dependencies with parameters

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What Symfony offers?

Service container● Overriding services in compiler passes with

the same interface or by extending the original one in Compiler Passes

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What Symfony offers?

Service container● Decorating services (new in Symfony 2.5)

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What Symfony offers?

Service container● Providing bundle configuration

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What Symfony offers?

Event dispatcher (mediator pattern)

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What Symfony offers?

You still can provide extension.There is no out of the box solution, because you don’t need it. You can check examples:● Twig● Form

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Conclusion

● Extensions helps you to make addition and modification of your application while minimizing impact to existing functionality.

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Conclusion

Common solutions● Abstractions and DI● Modular design● Extensions provider● Event-driven architecture

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Conclusion

Symfony offers● Bundles● Service container● Event dispatcher

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P.S.

Ideal OO code not the answer, because of performance.You can scale your infrastructure, because it's cheaper than development in some situations but usually not for a long time.

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References

● The Philosophy of Extensible Software● Github - PHP Design Patterns● Wikipedia - Extensibility● Wikipedia - List of software development philosophies● Wikipedia - SOLID● SO - Designing extensible software● Java Docs - Creating Extensible Applications● Symfony Books

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