Create contracts in laravel 5.4 - laravel

Question

Documentation on laravel.com is not sufficient. Can any one guide me through how to How To Create contracts in Laravel from scratch.
I need implementation of Contracts in Laravel. Right now, I'm using Laravel 5.4

Answer 1

Contract is just a fancy name for php interfaces. We have being using them all along and its not a new thing.
Contracts/Interfaces help us to maintain a loosely coupled code base. See the example from doc below.
<?php
namespace App\Orders;
class Repository
{
/**
* The cache instance.
*/
protected $cache;
/**
* Create a new repository instance.
*
* #param \SomePackage\Cache\Memcached $cache
* #return void
*/
public function __construct(\SomePackage\Cache\Memcached $cache)
{
$this->cache = $cache;
}
/**
* Retrieve an Order by ID.
*
* #param int $id
* #return Order
*/
public function find($id)
{
if ($this->cache->has($id)) {
//
}
}
}
Here when ever the Repository instantiate we should give a \SomePackage\Cache\Memcached instance in order for code to work. Hence our code is tightly coupled with \SomePackage\Cache\Memcached. Now look at below code.
<?php
namespace App\Orders;
use Illuminate\Contracts\Cache\Repository as Cache;
class Repository
{
/**
* The cache instance.
*/
protected $cache;
/**
* Create a new repository instance.
*
* #param Cache $cache
* #return void
*/
public function __construct(Cache $cache)
{
$this->cache = $cache;
}
}
Same thing but now we just need to provide some cache interface. And behind the scene you could have done something like this.
<?php
namespace App\Orders;
use Illuminate\Contracts\Cache\Repository as Cache;
class RedisCache implements Cache {
//
}
When above Repository instantiate, php will look at the Illuminate\Contracts\Cache\Repository and It has been implemented by RedisCache class.

Answer 2

I'm afraid Gayan's answer needs further elaboration to hit Rajan's question.
Yes Gayan is correct that creating a Contract class basically means creating a php interface.
Continuing the Cache example above, if we look into its source code (you can find it at this Github repo file), we can see something like this
<?php
namespace Illuminate\Contracts\Cache;
use Closure;
interface Repository
{
/**
* Determine if an item exists in the cache.
*
* #param string $key
* #return bool
*/
public function has($key);
/**
* Retrieve an item from the cache by key.
*
* #param string $key
* #param mixed $default
* #return mixed
*/
public function get($key, $default = null);
// the rest...
}
If we are using this interface in our laravel app, it is said to be a "Contract". It is declaring what methods/properties a class should have if it implements this interface. For example in our app...
<?php
namespace App\Whatever;
use Illuminate\Contracts\Cache\Repository;
class Foo implements Repository {
//
}
Then class Foo will need to have methods has and get in order to fulfil what has been stated in the Repository contract.