类名作为公共函数中的参数

What's the difference between:

class PostController extends \BaseController {
      public function delete($id) {
        $deletePost = Post::findOrFail($id);
        return View::make('backend.delete')->with('post', $deletePost);
      }
}

and

class PostController extends \BaseController {
      public function delete(Post $post) {
        return View::make('backend.delete')->with('post', $post);
      }
}

Can somebody explain to me: public function delete(Post $post)

we are taking a Class named "Post" as a variable $post?

UPDATE1.

in routes.php:

Route::model('post', 'Post');

Route::get('delete/{post}', array('uses' => 'PostController@delete'));
Route::post('delete', array('uses' => 'PostController@doDelete'));

and in PostController.php:

public function delete(Post $post) {
    return View::make('backend.delete')->with('post', $post);
}

public function doDelete() {
    $post = Post::findOrFail(Input::get('id'));
    $post->delete();

    return Redirect::action('PostController@home');
}

but anyway i get an error: No query results for model [Post]. with the 2nd method.

It's just a type hinting:

"Type hinting means that whatever you pass must be an instance of (the same type as) the type you're hinting."

In your example it's Post:

public function delete(Post $post) { /* code */ }

It's just checks $post variable whether instance it or not. So everything looks good in your code. And it should work.

They both achieve the same thing of giving you the model (if it exists).

The second way is called Route Model binding. Route model binding provides a convenient way to inject model instances into your routes.

To bind a model to a route:

Route::model('post', 'Post');

Next, define a route that contains a {user} parameter:

Route::get('delete/{post}', array('uses' => PostController@delete));

So we have bound the {post} parameter to the Post model, a Post instance will be injected into the route.

This means if someone reaches your delete() function - they have already provided a valid Post model - which is the equivalent of Post::findOrFail($id)