Laravel View Composer - php

Question

I'm following a tutorial for laravel and there is something that I don't understand. It's referred to using views composer.
-I have a template called from app/http/routes.php given an Url:
Route::get('cats/create', function(){return view('cats.create');});
this is cats/create.blade.php:
#extends('master')
#section('header')
<h2> Add a new cat </h2>
#stop
#section('content')
{!! Form::open(['url'=>'/cats']) !!}
#include('partials.forms.cat')
{!! Form::close() !!}
#stop
-This template includes another one (partial) which covers the HTML of a Form
<div class="form-group">
{!! Form::label('name','Name') !!}
<div class="form-controls">
{!! Form::text('name', null, ['class' => 'form-control']) !!}
</div>
</div>
<div class="form-group">
{!! Form::label('date_of_birth', 'Date of Birth') !!}
<div class="form-controls">
{!! Form::date('date_of_birth', null, ['class' => 'form-control']) !!}
</div>
</div>
<div class="form-group">
{!! Form::label('breed_id','Breed') !!}
<div class="form-controls">
{!! Form::select('breed_id', $breeds, null, ['class' => 'form-control']) !!}
</div>
</div>
{!! Form::submit('Save Cat', ['class' => 'btn-primary']) !!}
-Now uses a view composer in order to automatically fullfill the select element when this partial view is called. In AppServiceProvider:
public function boot(ViewFactory $view)
{
$view->composer('partials.forms.cat','Furbook\Http\Views\Composers\CatFormComposer');
}
4.- And this is that CatFormComposer
class CatFormComposer
{
protected $breeds;
public function __construct(Breed $breeds)
{
$this->breeds = $breeds;
}
public function compose(View $view) {
$breeds = $this->breeds;
$view->with('breeds', $breeds->lists('name', 'id'));
}
}
It works. What I don't get is, How is that $breeds parameter being passed to the constructor of the class?

Answer 1

All View Composers are resolved by laravel service container. So when you type-hint Breed $breeds laravel will use php reflection api to find the expected class and inject the instance of that class (in that case: Container will find Breed class , create new Breed and pass the instance on constructor).
Also for deeper understanding you can take look about service locator pattern