Laravel 中服务容器的概念是什么

Laravel中的Service Container是一个依赖注入容器和应用程序的注册表

The advantages of using a Service Container over creating manually your objects are:

Ability to manage class dependencies on object creation

You define how a object should be created in one point of the application (the binding) and every time you need to create a new instance, you just ask it to the service container, and it will create it for you, along with the required dependencies

For example, instead of creating objects manually with the new keyword:

//every time we need YourClass we should pass the dependency manually
$instance = new YourClass($dependency);

you can register a binding on the Service Container:

//add a binding for the class YourClass 
App::bind( YourClass::class, function()
{
    //do some preliminary work: create the needed dependencies
    $dependency = new DepClass( config('some.value') );

    //create and return the object with his dependencies
    return new YourClass( $dependency );
});

并通过服务容器创建一个实例:

//no need to create the YourClass dependencies, the SC will do that for us!
$instance = App::make( YourClass::class );

Binding of interfaces to concrete classes

使用Laravel automatic dependency injection，当应用程序的某些部分(即控制器的构造函数)需要接口时，服务容器会自动实例化一个具体的类.更改绑定上的具体类将更改通过所有应用程序实例化的具体对象:

//everityme a UserRepositoryInterface is requested, create an EloquentUserRepository 
App::bind( UserRepositoryInterface::class, EloquentUserRepository::class ); 

//from now on, create a TestUserRepository 
App::bind( UserRepositoryInterface::class, TestUserRepository::class );

Using the Service Container as a Registry个

You can create and store unique object instances on the container and get them back later: using the App::instance method to make the binding, and thus using the container as a Registry.

// Create an instance.
$kevin = new User('Kevin');

// Bind it to the service container.
App::instance('the-user', $kevin);

// ...somewhere and/or in another class...

// Get back the instance
$kevin = App::make('the-user'); 

As a final note, essentially the Service Container -is- the Application object: it extends the Container class, getting all the container's funtionalities