Get the quick and dirty (and simple!) scoop on the Dependency Injection design pattern. From Columbus PHP Meetup.

1. Dependency
Injection
Flash Talk by John Dillick

2. What is DI?
Dependency Injection is an “inversion of control”
pattern that avoids tight coupling of a dependent
object to its dependencies.

3. What does this mean in
English?

4. Pass objects in.
Instead of instantiating needed objects inside your
class, pass those needed objects in.
Do this:
● In your class constructor
● On a setter method

5. Without DI
// Foo is my dependency
function myFunction() {
$foo = new Foo;
return $foo->bar();
}
$bar = myFunction();

6. With DI
function myFunction(Foo $foo) {
return $foo->bar();
}
// Foo “injected”
$bar = myFunction(new Foo);

7. Why would I do this?

8. Benefits
➔ Single Responsibility
Because your class needn’t be
concerned with creating things to work.
➔ Flexibility
You class just “uses” things it’s passed,
so you can pass it other things without
changing the implementation.
➔ Clarity
You can see up front what the
dependencies of your class are..
➔ Testable
Easier to Unit Test your class if your
tests can control dependencies.

9. Example Code
https://github.com/jdillick/di-example

10. Fin.