Instantiation of reference classes within reference classes - problems with lock() and immutability - r

Question

I have come across some behaviour from R reference classes I would like to work around. In the following code, reference class B has two fields of reference class A in it.
These fields in B appear to be instantiated (possibly twice) with a zero-argument (default) versions of reference class A before B's initialize() method is called. These instances are then replaced with the correct versions of instance A during B's initialization process. The problem is that if I use lock() from B's instance generator, the initial empty instantiation's of A cannot be replaced in B. Another problem is that reference class A needs a default value in initialize [or a missing(c) test].
Help - suggestions - etc. appreciated.
A <- setRefClass('A',
fields = list(
count = 'numeric'
),
methods = list(
initialize = function (c=0) {
cat('DEBUG: A$initialize(c); where c='); cat(c); cat('\n')
count <<- c
}
)
)
instance.of.A <- A$new(10)
str(instance.of.A)
B <- setRefClass('B',
field = list(
a = 'A',
b = 'A'
),
methods = list(
initialize = function(c) {
a <<- instance.of.A
b <<- getRefClass('A')$new(c)
}
)
)
instance.of.b <- B$new(100)
str(instance.of.b)

Answer 1

Here are two possible solutions:
Don't set fields attribute:
B <- setRefClass('B',
methods = list(
initialize = function(c) {
.self$a = instance.of.A
.self$b =getRefClass('A')$new(c)
}
)
)
Set fields, but use the ANY class:
B <- setRefClass('B',
field = (a="ANY", b="ANY"),
methods = list(
initialize = function(c) {
a <<- instance.of.A
b <<- getRefClass('A')$new(c)
}
)
)
The downside of both these solutions is the type isn't enforced in a and b, i.e.
B$a = "Fred"
is now possible.

Answer 2

Drawing on the above, the solution I am using is (a little long because of the type checking):
A <- setRefClass('A',
fields = list(
count = function(x) {
if (!missing(x)) {
if(class(x) != 'numeric')
stop('Class A: count set by non-number')
.self$count.private <- x
}
.self$count.private
}
),
methods = list(
initialize = function (c=0) {
cat('DEBUG: A$initialize(c); where c='); cat(c); cat('\n')
count <<- c
}
)
)
instance.of.A <- A$new(10)
str(instance.of.A)
B <- setRefClass('B',
field = list(
a = function(x) {
if (!missing(x)) {
if(!inherits(x, 'envRefClass') || class(x)[1] != 'A')
stop('Class B: expecting instance of class A')
.self$a.private <- x
}
.self$a.private
},
b = function(x) {
if (!missing(x)) {
if(!inherits(x, 'envRefClass') || class(x)[1] != 'A')
stop('Class B: expecting instance of class A')
.self$b.private <- x
}
.self$b.private
}
),
methods = list(
initialize = function(c) {
a <<- instance.of.A
b <<- getRefClass('A')$new(c)
}
)
)
instance.of.b <- B$new(100)
str(instance.of.b)