Strategy design pattern presentation
tl;dr: Program to an interface, not an implementation
Wait, strategy?
WTF is that?
a careful plan or method for achieving a particular goal.
No battle plan ever survived first contact with the enemy. (Murphy's law of combat, or more accurately Von Moltke, a Prussian general during Bismark era)
Real life example
The Strategy pattern allows you to have multiple strategies to solve one problem.
Its motto is the following:
Program to an interface, not an implementation
Ok, Ok... real real life example.
Existing class
class PresentationBuilder
{
public function createPresentation($keywords)
{
$imageSearch = new SearchImageTool();
$this->images = $imageSearch->find($keywords);
// ...
}
}Quick fix
class PresentationBuilder
{
public function createPresentation($keywords, $isWd)
{
if ($isWd) {
$imageSearch = new ImprovedImageSearch();
} else {
$imageSearch = new NormalImageSearch();
}
$this->images = $imageSearch->find($keywords);
// ...
}
}class PresentationBuilder {
protected $imageSearcher;
public function __construct(ImageSearchInterface $imageSearcher) {
$this->imageSearcher = $imageSearcher;
}
public function createPresentation($keywords) {
$images = $this->imageSearch->find($keywords);
// ...
}
}
interface ImageSearchInterface {
public function findByKeywords($keywords);
}
class ImprovedImageSearch implements ImageSearchInterface {
public function findByKeywords($keywords) {
// Go get images from BonjourMadame.
}
}
class NormalImageSearch implements ImageSearchInterface {
public function findByKeywords($keywords) {
// Go get images from Google
}
}The images are good, but the code is bad...
Beware the Pattern!
// Presentation for WD Strategy Pattern
$presentationBuilder = new PresentationBuilder(new ImprovedImageSearch());
$presentation = $presentationBuilder->createPresentation('Strategy pattern');Now I just have to decide in my own project which strategy to use.
And, if someone more into bananas are not happy with the 2 provided strategies, they can build their own easily:
class BananaImageSearch implements ImageSearchInterface {
public function findByKeywords($keywords) {
// Go get images from some banana picture bank.
}
}
$presentationBuilder = new PresentationBuilder(new BananaImageSearch());
$presentation = new $presentationBuilder->createPresentation('Banana split');Pros
- Integrates nicely with dependency injections
- Allow flexibility for reusers of your package
- Avoid an ugly switch/case
- Strategies are reusable in other contextes
Cons
- Users must be aware of the different strategies
- Add a new dependency
- All strategies must implement the same interface; that's sometime hard to achieve
Strategy Design Pattern
By fguery
