protobuf optional

Protobuf (Protocol Buffers) is a language-agnostic data serialization format developed by Google. In Protobuf, the `optional` keyword is used to define optional fields in the generated code. Optional fields allow you to have fields that may or may not be present in a Protobuf message.

When you define a field as optional in Protobuf, it means that the field can be omitted when serializing a message. If the field is not set, it will not be included in the serialized data. When deserializing a message, if an optional field is not present in the serialized data, its value will be set to its default value.

Here's an example of defining an optional field in a Protobuf message using the `optional` keyword:

message MyMessage {
  optional int32 my_field = 1;
}

In this example, `my_field` is defined as an optional field of type `int32`. It can be omitted when serializing a `MyMessage` instance, and its default value will be set if it is not present during deserialization.

It's worth mentioning that starting from Protocol Buffers version 3 (Protobuf3), all fields are considered optional by default. The `optional` keyword is no longer required and can be omitted.