This document discusses dependency inversion and dependency injection principles in software design. It explains that high-level modules should depend on low-level modules through abstractions rather than concrete implementations. This allows for loose coupling between modules and makes them easier to test and maintain. The document provides examples of dependency injection in PHP code and describes how Laravel's service container implements dependency injection through binding abstractions to concrete classes and resolving dependencies through the container.

1. Dependency Inversion
Dependency Injection
Contract
SOLID
Service Provider
Service Container
IoC
DI

2. Dependency Inversion
SOLID
High-level modules should not depend on
low-level modules. Both should depend
on abstractions.
http://en.wikipedia.org/wiki/Dependency_inversion_principle

3. ⾼高階模組不應該依賴低階模組。
兩者都應該要依賴於抽象
What the …

4. class UserModify {
public function __constructor() {
$this->storage = new MysqlStorage();
}
public function modify($data) {
$result = $this->storage->save($data);
return $result;
}
}
⾼高階直接依賴低階

6. class UserModify {
public function __constructor(DataStorageInterface $storage) {
$this->storage = $storage;
}
public function modify($data) {
$result = $this->storage->save($data);
return $result;
}
}
class MysqlStorage implements DataStorageInterface {
public function save($data){ // …. }
}
interface DataStorageInterface {
public function save(array $data);
}
Abstraction
Low Level Module
Hight Level Module

7. Why

8. #隱藏低階模組的細節
#容易抽換實作
#程式碼變多
#追蹤⽐比較困難
#讓測試變容易 #⽐比較不直覺

9. 隱藏低階模組的細節
class UserModify {
public function __constructor() {
$dbConfig = [….];
$this->storage = new MysqlStorage($dbConfig);
}
}

10. 容易抽換實作
class UserModify {
public function __constructor(DataStorageInterface $storage) {
$this->storage = $storage;
}
}
class SqliteStorage implements DataStorageInterface {
public function save($data){ // …. }
}
SqliteStorage Instance

11. 讓測試變容易
class DummyStorage implements DataStorageInterface {
public function save() { return ‘Success’; }
}
class UserModify {
public function modify($data) {
return $this->storage->save($data);
}
}
class UserModifyTest {
public function it_return_new_instance_after_modify($data) {
$instance = new UserModify(new DummyStorage);
$result = $instance->modify();
assert($result, ‘Success’);
}
}

12. How

13. Inverse of Control
http://zh.wikipedia.org/wiki/%E6%8E%A7%E5%88%B6%E5%8F%8D%E8%BD%AC

14. Dependency Injection
http://en.wikipedia.org/wiki/Dependency_injection
Dependency injection is a software design
pattern that implements inversion of control for
software libraries, where the caller delegates to
an external framework the control flow of
discovering and importing a service or software
module.

15. Service
Provider
Container

17. http://laravel.tw/docs/5.0/providers
Service Provider

18. .
├── AppServiceProvider.php
├── BusServiceProvider.php
├── ConfigServiceProvider.php
├── EventServiceProvider.php
├── FilterServiceProvider.php
├── RepoServiceProvider.php
└── RouteServiceProvider.php
app/Providers

19. <?php namespace BackendProviders;
use IlluminateSupportServiceProvider;
class AppServiceProvider extends ServiceProvider {
public function register() {
$this->app->bind(
‘Jaster/Interfaces/FooInterface’,
‘Jaster/Implements/FooImplementClass’
);
}
}
app/Providers/AppServiceProvider.php

20. 'providers' => [
/*
* Laravel Framework Service Providers...
*/
'IlluminateFoundationProvidersArtisanServiceProvider',
'IlluminateAuthAuthServiceProvider',
'IlluminateBusBusServiceProvider',
'IlluminateCacheCacheServiceProvider',
'IlluminateFoundationProvidersConsoleSupportServiceProvider',
'IlluminateRoutingControllerServiceProvider',
// ….
],
config/app.php

21. Service Container
The Laravel service container is a powerful tool
for managing class dependencies. Dependency
injection is a fancy word that essentially means
this: class dependencies are "injected" into the
class via the constructor or, in some cases,
"setter" methods.
http://laravel.com/docs/5.0/container

22. Trace initialize of service container ( IlluminateFoundationApplication )
IlluminateFoundationApplication::__construct
IlluminateFoundationApplication::registerBaseBindings
IlluminateFoundationApplication::registerBaseServiceProviders
IlluminateFoundationApplication::registerCoreContainerAliases

23. Trace register of IlluminateContractsHttpKernel
bootstrap/app.php
$app->singleton(‘IlluminateContractsHttpKernel', 'AppHttpKernel');
IlluminateFoundationApplication::singleton
IlluminateFoundationApplication::bind

24. Trace how to use IlluminateContractsHttpKernel
$kernel = $app->make('IlluminateContractsHttpKernel');
public/index.php
IlluminateFoundationApplication::make
IlluminateContainerContainer::make
IlluminateContainerContainer::build

25. Trace Facade autoloader
IlluminateFoundationHttpKernel::bootstrap
IlluminateFoundationApplication::bootstrapWith
IlluminateFoundationBootstrapRegisterFacades
IlluminateFoundationAliasLoader::register
IlluminateFoundationAliasLoader::prependToLoaderStack

26. PHP UK Conference 2014 - Stephan Hochdorfer -
The 7 Deadly Sins of Dependency Injection
https://www.youtube.com/watch?v=hMix8gfDy54

27. Thank you