Error when making generator a method of an R6 class

[dfalbel]

Not sure if you want to support that, but the following does not work:

g <- R6::R6Class(
  "generator",
  public = list(
    x = coro::generator(function() {
      for (i in 1:10)
        yield(i)
    })
  )
)

instance <- g$new()
instance$x
#> <generator>
#> Error in env_get(fn_env(x), "fn", inherit = TRUE): argument "default" is missing, with no default
instance$x()
#> Error in dots_split(..., .n_unnamed = 0:1): object '_parent' not found

R6 changes the function environments to the class env. It's probably also removing important information from the generator function.

[lionel-]

Maybe there should be a way of preventing R6 from treating a function as a method? For example functions wrapped in I(). And maybe functions with a custom class should automatically get that treatment?

Relatedly, maybe R6Class() should issue a warning when methods don't inherit from the current environment? Changing their environments in the background seems a bit unsafe.

What do you think @wch?

[lionel-]

In the meantime you can wrap the generators like this @dfalbel

R6::R6Class(
  "generator",
  private = list(
    generators = list(x = coro::generator(function() {
      for (i in 1:10)
        yield(i)
    }))
  ),
  public = list(
    x = function() private$generators$x()
  )
)

[dfalbel]

Thanks! That works great for me!

[wch]

With R6Class, all functions that are part of public or private are assumed to be methods, and their environment is modified when the class is instantiated.

R6 does have the notion of members function that are not methods, though. They must be assigned either in initialize() or after the object is created. So you could so something like this:

num_generator <- coro::generator(function() {
  for (i in 1:10)
    yield(i)
})

Generator <- R6::R6Class(
  "Generator",
  public = list(
    initialize = function() {
      self$x = num_generator
    },
    x = NULL
  )
)

(You could also call coro::generator(function() ....) inside of initialize(), but that would create a new factory for each instance, which is less efficient.)

The difference between methods and non-method functions is recognized when the object is cloned; in the cloned object, methods will have their environment changed (so they can find the correct self and private), but non-method functions will not have their environment changed.

@lionel-, the idea of using I() to mark non-method functions is interesting. Want to file an issue on R6 so it can be discussed there? Or maybe the current behavior just needs to be better documented.

[lionel-]

Thanks for your input @wch!
I've filed an issue for I() at r-lib/R6#222.

Closing this since it's not a coro issue.