add non-copying asdict function

selfdrive/car/card.py

@@ -60,6 +60,24 @@ def can_comm_callbacks(logcan: messaging.SubSocket, sendcan: messaging.PubSocket
   return can_recv, can_send
 
 
+def asdict(obj) -> dict[str, any]:
+  """Note that this function returns references rather than copies where possible"""
+
+  if not dataclasses.is_dataclass(obj):
+    raise TypeError("asdict() should be called on dataclass instances")
+
+  def _asdict_inner(obj: any) -> dict[str, any]:
+    if dataclasses.is_dataclass(obj):
+      ret = {}
+      for f in dataclasses.fields(obj):
+        ret[f.name] = _asdict_inner(getattr(obj, f.name))
+      return ret
+    else:
+      return obj
+
+  return _asdict_inner(obj)
+
+
 def convert_to_capnp(struct: structs.CarParams | structs.CarState | structs.CarControl.Actuators) -> capnp.lib.capnp._DynamicStructBuilder:
   struct_dict = dataclasses.asdict(struct)
 
@@ -74,8 +92,10 @@ def convert_to_capnp(struct: structs.CarParams | structs.CarState | structs.CarC
     setattr(struct_capnp.lateralTuning, which, lateralTuning_dict)
   elif isinstance(struct, structs.CarState):
     struct_capnp = car.CarState.new_message(**struct_dict)
-  else:
+  elif isinstance(struct, structs.CarControl.Actuators):
     struct_capnp = car.CarControl.Actuators.new_message(**struct_dict)
+  else:
+    raise ValueError(f"Unsupported struct type: {type(struct)}")
 
   return struct_capnp