01_definitions__user.proto

syntax = 'proto3';

message User {
  string first_name = 1;
  string last_name = 2;
}

02_main.rb

require_relative './lib/user_pb'
require 'ap'


-> {
  user = User.new(first_name: "Taro", last_name: "Yamada")
  ap user.first_name
  ap user.last_name

  user.first_name = "Tanaka"
  ap user.first_name

  encoded_data = User.encode(user)

  File.write("user.proto.encoded", encoded_data)

  user2 = User.decode(encoded_data)
  ap user2
  ap user2.to_json
}.call

$bundle ruby protobuf_sample.rb
"Taro"
"Yamada"
"Tanaka"
{
    :first_name => "Tanaka",
     :last_name => "Yamada"
}
"{\"firstName\":\"Tanaka\",\"lastName\":\"Yamada\"}"