The Singleton Dilemma

The Singleton Dilemma

Frank SonsSenior PHP Engineer CTD

The Singleton Dilemma

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What is a Singleton?

What is the problem?

What is the solution to this dilemma?

Singleton? What‘s that?

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Singleton? Tell me more…

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Probably best known design pattern

Only one instance of a class at any time

Global access to that single instance

How to implement a Singleton in PHP?

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How to use the Singleton?

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So, it is really cool, isn‘t it?

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Singleton and PHP are no friends

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Singleton: unique instance for application

PHP: Shared-Nothing architecture

Dilemma: instance only unique for request

Singleton has even more problems

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Dependency hiding

Globals are bad, singleton is a global

No Unit Testing possible

Is there a solution?

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Solution: Just create one!

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Code Convention: just create one

Trust your Team members!

Solution: Dependency Injection

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Create one instance and „inject“ it

Objects should be loosely coupled

Don‘t create objects in regular classes

„Ask, don‘t look“

Solution: Dependency Injection

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Solution: Factory

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Encapsulates object creation

Different factories for different lifetimes

Handles object lifetimes

Solution: Factory

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Solution: PHP application lifetime

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Cache or Session for „application“ lifetime

Factory can handle Cache or Session

„Friends don‘t let friends do Singleton“

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Benefits!

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Unit Testing is possible!

Easy object creation!

Better lifetime handling!

Easy to change dependencies!

And about the good Singleton…

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The only good Singleton…

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Thank you!

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Find us on

Bigpoint GmbHFrank Sons

Senior Software Engineer CTD

Drehbahn 47-4820354 Hamburg

Germany

Tel +49 40.88 14 13 - 0Fax +49 40.88 14 13 - 11

[email protected]

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