Add lazy props feature

Author: reinink

src/LazyProp.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Inertia;
+
+use Illuminate\Support\Facades\App;
+
+class LazyProp
+{
+    protected $callback;
+
+    public function __construct(callable $callback)
+    {
+        $this->callback = $callback;
+    }
+
+    public function __invoke()
+    {
+        return App::call($this->callback);
+    }
+}

src/Response.php

@@ -54,9 +54,15 @@ public function toResponse($request)
 
         $props = ($only && $request->header('X-Inertia-Partial-Component') === $this->component)
             ? Arr::only($this->props, $only)
-            : $this->props;
+            : array_filter($this->props, function ($prop) {
+                return ! ($prop instanceof LazyProp);
+            });
 
         array_walk_recursive($props, function (&$prop) use ($request) {
+            if ($prop instanceof LazyProp) {
+                $prop = App::call($prop);
+            }
+
             if ($prop instanceof Closure) {
                 $prop = App::call($prop);
             }

src/ResponseFactory.php

@@ -54,6 +54,11 @@ public function getVersion()
         return (string) $version;
     }
 
+    public function lazy(callable $callback)
+    {
+        return new LazyProp($callback);
+    }
+
     public function render($component, $props = [])
     {
         if ($props instanceof Arrayable) {