protobuf oneof

Protobuf `oneof` is a feature that allows you to define a field that can have one and only one value out of a set of options. It's useful when you have a group of fields and you want to ensure that only one of them is set at any given time. This can help save space in the encoded message and simplify the validation logic.

To use `oneof` in Protobuf, you define it within a message definition. Here's an example:

message MyMessage {
  oneof my_field {
    int32 option1 = 1;
    string option2 = 2;
    bool option3 = 3;
  }
}

In this example, the `my_field` is a `oneof` field that can have three options: `option1`, `option2`, and `option3`. Only one of these options can be set within an instance of `MyMessage`. When serializing this message, only the selected option will be included in the encoded data.

To access or set the value of the `oneof` field, you can use the corresponding getter and setter methods generated by the Protobuf compiler for your chosen programming language. The compiler generates methods like `has_my_field()` to check if a specific option is set, and `my_field()` to retrieve the value.

Keep in mind that once a value is set for a `oneof` field, setting another option will automatically clear the previous value.