Added overload function for allowing dynamic properties

README.md

@@ -130,6 +130,26 @@ class WelcomeMail extends TemplateMailable
 
 By extending the `\Spatie\MailTemplates\TemplateMailable` class this mailable will be rendered using the corresponding `MailTemplate`. All public properties on the `WelcomeMail` will be available in the template.
 
+If you need to use properties within your template that are initially defined within your `WelcomeMail` (for example, data that comes from another source). You can call `$this->setAdditionalData()` and pass it an array of you additional key => value pairs.
+
+An example of this would be:
+```php
+namespace App\Mail;
+
+use TemplateMailable;
+
+class WelcomeMail extends TemplateMailable
+{
+
+    public function __construct(User $user)
+    {
+        $this->setAdditionalData([
+            'name' => 'Joe Bloggs'
+        ]);
+    }
+}
+```
+
 ### Customizing the `MailTemplate` model
 
 The default `MailTemplate` model is sufficient for using _one_ database mail template for _one_ mailable. If you want to use multiple mail templates for the same mailable _or_ extend the `MailTemplate` model, we highly encourage you to publish the `mail_template` migration and create your own mail template model by extending `MailTemplate`. Make sure to implement the `MailTemplateInterface` interface as well.

src/TemplateMailable.php

@@ -17,6 +17,9 @@ abstract class TemplateMailable extends Mailable
     /** @var MailTemplateInterface */
     protected $mailTemplate;
 
+    /** @var array */
+    protected $additionalData;
+
     public static function getVariables(): array
     {
         return static::getPublicProperties();
@@ -111,4 +114,17 @@ protected function getMailTemplateRenderer(): TemplateMailableRenderer
     {
         return app(TemplateMailableRenderer::class, ['templateMailable' => $this]);
     }
+
+    public function buildViewData(): array
+    {
+        $mailablePropeties = parent::buildViewData();
+        if(is_null($this->additionalData)) {
+            return $mailablePropeties;
+        }
+        return array_merge($mailablePropeties, $this->additionalData);
+    }
+
+    public function setAdditionalData($array) {
+        $this->additionalData = $array;
+    }
 }