R: proto serialization/deserialization to list

Question

I'd like to be able to store some simple proto objects in a persistent store (MongoDB) where their properties can be manipulated by code from other programming languages. By simple I mean that they will not refer to other proto objects. Their properties will be common R types: lists, vectors, etc. Further, each object can have a factory method that creates it given a list with its property values. Therefore the MongoDB-to-proto path seems straightforward.

I don't understand proto's internals and R environment chaining well-enough to know whether there is a simple and robust way to get all the proto object's properties as an R list. Can this be done automatically or should I be thinking about all proto objects implementing something like a to_list() method?

Some example code using testthat and a new MongoDB driver API I am developing about the behavior I'd like to see here:

test_that("proto persistence", {
  Person <- proto(
    ..Name = 'PersonFactory',
    has_tag = function(., tag) { 
     tag %in% .$tags 
    },
    new = function(., name, tags=c()) {
     .$proto(..Name='Person', name=name, tags=tags)
    } 
  )

  p1 <- Person$new(name='bob', tags=c('friend', 'coworker'))

  coll <- test_db()$collection('test') 
  coll$store('bob', p1)

  result <- coll$find_one(id='bob')
  expect_true(is.list(result))
  expect_true(is.list(result$proto))
  expect_equal(result$proto$name, 'bob')
  expect_equal(result$proto$tags, c('friend', 'coworker'))

  p2 <- coll$load('bob')
  expect_equal(p2$name, 'bob')
  expect_equal(p2$tags, c('friend', 'coworker'))
  expect_true(p2$has_tag('friend'))
})

Answer 1

To turn p1 from the question into a list. L1 :

L1 <- as.list(p1)

and to turn it back into a proto object, p1a, whose parent is Person :

p1a <- as.proto(L1, parent = Person)

You can then build whatever structure you want around these basics.