protobuf optional mutable

Protobuf (Protocol Buffers) is a language-agnostic serialization format developed by Google. In Protobuf, the "optional" keyword is used to define a field in a message as optional, meaning it may or may not be present in an instance of that message.

The "mutable" keyword, on the other hand, is not specific to Protobuf. It generally refers to the ability to modify an object's state after it has been created. In the context of Protobuf, when you have an optional field that is also marked as "mutable," it means that you can change the value of that field in the generated code.

For example, let's say you have a Protobuf message definition with an optional field called "name":

message Person {
  optional string name = 1;
}

In your code, if you mark the "name" field as mutable, you can modify its value later on:

Person person;
person.mutable_name()->assign("John"); // Set the name to "John"
person.mutable_name()->assign("Alice"); // Update the name to "Alice"

Using the "mutable" keyword provides flexibility in modifying optional fields in Protobuf messages.