Created share() method for CompositeContext class

README.md

@@ -386,6 +386,49 @@ The `$this->getContext(...)` call is a convenient alternative to `$this->context
 
 Unlike a normal interactor, the `call()` method on an organizer is already implemented. When called, this organizer will perform interactors in the order they were pushed onto the queue in the `organize()` method.
 
+### Sharing an attribute between Contexts
+
+Suppose you have to retrieve the User (using a `Deefour\Interactor\Interactor`) and then share this user attribute with CreateVehicleContext. You are able to achieve this by using `share()` method from `Deefour\Interactor\CompositeContext`.
+
+```php
+use Deefour\Interactor\Organizer;
+
+class RegisterUser extends Organizer
+{
+    /**
+     * Constructor.
+     *
+     * @param RegisterUserContext $context A composite context for the organizer.
+     */
+    public function __construct(RegisterUserContext $context)
+    {
+        parent::__construct($context);
+    }
+
+    /**
+     * Create the new user and their first vehicle.
+     */
+    public function organize()
+    {
+        $createUserInteractor = new CreateUser($this->getContext(CreateUserContext::class));
+        $createUserContext = $createUserInteractor->call();
+
+        /**
+         * Shares attribute 'user' from CreateUserContext with CreateVehicleContext.
+         */
+        $this->context()->share(
+            CreateUserContext::class,
+            CreateVehicleContext::class,
+            'user'
+        );
+
+        $this->addInteractor(new CreateVehicle($this->getContext(CreateVehicleContext::class)));
+    }
+}
+```
+
+This way, the Interactor `CreateVehicle` is able to get the `User` from `CreateVehicleContext`, if necessary.
+
 ### Executing an Organizer
 
 An organizer is executed like any other interactor. Call the `call()` method to kick things off after instantiation.

src/CompositeContext.php

@@ -31,6 +31,25 @@ public function __construct(array $contexts)
         parent::__construct($contexts);
     }
 
+    /**
+     * Shares $attribute from $contextSrc with $contextDest
+     *
+     * @param  string $contextSrc   The context FQCN to get $attribute from (source)
+     * @param  string $contextDest  The context FQCN to share $attribute with (destination)
+     * @param  string $attribute    The attribute name as a string
+     *
+     * @return void
+     */
+    public function share($contextSrc, $contextDest, $attribute)
+    {
+        $contextSrc  = $this->get($contextSrc);
+        $contextDest = $this->get($contextDest);
+
+        if (isset($contextSrc) && isset($contextDest) && isset($contextSrc->{$attribute})) {
+            $contextDest->{$attribute}($contextSrc->{$attribute});
+        }
+    }
+
     /**
      * Type-check each context in the source array provided to the composite.
      * Throw an exception if an argument does not subclass the base context.