How to change nested elements (cannot borrow data in dereference...)

[manio]

Hi,
I have the following protobuf structure (print_to_string_pretty):

services {
  id: 1
  media_sink_service {
    available_type: MEDIA_CODEC_VIDEO_H264_BP
    video_configs {
      codec_resolution: VIDEO_800x480
      frame_rate: VIDEO_FPS_30
      width_margin: 0
      height_margin: 0
      density: 160
      decoder_additional_depth: 2
      viewing_distance: 950
      pixel_aspect_ratio_e4: 10000
    }
  }
  [...]

I created it like with:
let mut x = ServiceDiscoveryResponse::parse_from_bytes(&payload[2..]).unwrap();

Now I want to change the density parameter, so I am calling:
x.services[0].media_sink_service.video_configs[0].set_density(80);

But the compiler is screaming at me:

error[E0596]: cannot borrow data in dereference of `MessageField<mitm::protos::MediaSinkService>` as mutable
   --> src/mitm.rs:244:5
    |
244 |     x.services[0].media_sink_service.video_configs[0].set_density(129);
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable
    |
    = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `MessageField<mitm::protos::MediaSinkService>`

The protobuf definition is here

Please help me to solve this problem. Or tell me a proper way to do it...

[manio]

I searched for DerefMut in issues and encounter this: #54
Thanks to that issue I've added as_mut() to have a call like this:

x.services[0].media_sink_service.as_mut().unwrap().video_configs[0].set_viewing_distance(80);

And it seems this was it! :)