Why the message classes generated by the protocol buffer compiler are all immutable?

Question

The protocol buffer compiler generated message classes are immutable. The message classes contain appropriate setter methods but no getter methods on it. This constraint does not apply to other serialization technologies like Java binary serialization, XML, JSON, etc.

As per my understanding, immutability is of use while doing concurrent programming. Immutability could be of help in achieving thread-safety. But, I assume, that is not the reason in case of protocol buffer.

What could be the reason of making message classes immutable?

After reading the protocol buffer documentation, it seems the above stated only applies to Java (at the least) and not to C++ and other supported platforms/languages.

Note: This question is only to satisfy my curiosity.

Thanks.

Answer 1

The google implementation indeed uses a builder pattern - i.e. a mutable (but not very usable in terms of entity) builder, which creates an immutable object instance. This is not a requirement - indeed, there are alternative implementations for several platforms that do not use this design pattern. But frankly, it simply isn't an issue, because if there is any friction (and what you describe: friction) then you should simply avoid using your DTO types (i.e. the objects used for serialization) as your primary domain entity types. As soon as you do that, it becomes a non-issue: you write your own domain entity types with whatever pattern you like (including any domain logic etc), and then map to/from the DTO types as and when you need to; then the choice of design pattern used by the DTO tier is a mere uninteresting implementation detail.

But again: for your chosen platform, take a look to see if any alternative implementations might suit your requirements more closely.