the singleton dilemma
TRANSCRIPT
The Singleton Dilemma
Frank SonsSenior PHP Engineer CTD
The Singleton Dilemma
2
What is a Singleton?
What is the problem?
What is the solution to this dilemma?
Singleton? What‘s that?
3
Singleton? Tell me more…
4
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?
5
How to use the Singleton?
6
So, it is really cool, isn‘t it?
7
Singleton and PHP are no friends
8
Singleton: unique instance for application
PHP: Shared-Nothing architecture
Dilemma: instance only unique for request
Singleton has even more problems
9
Dependency hiding
Globals are bad, singleton is a global
No Unit Testing possible
Is there a solution?
10
Solution: Just create one!
11
Code Convention: just create one
Trust your Team members!
Solution: Dependency Injection
12
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
13
Solution: Factory
14
Encapsulates object creation
Different factories for different lifetimes
Handles object lifetimes
Solution: Factory
15
Solution: PHP application lifetime
16
Cache or Session for „application“ lifetime
Factory can handle Cache or Session
„Friends don‘t let friends do Singleton“
17
Benefits!
18
Unit Testing is possible!
Easy object creation!
Better lifetime handling!
Easy to change dependencies!
And about the good Singleton…
19
The only good Singleton…
20
Thank you!
21
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
23