S3 Methods

This is probably a crucial example as it demonstrates one great way to use Vapour. R's S3 dispatch methods are very common in R and in fact somewhat resembles the idea of "types:" dispatching methods based on an object class.

Assume we're working with a simple database, we need to fetch users from the database, update the users table, etc (CRUD). We should probably define a user object that would allow us to ensure we always work with the right structure, and expected types.

note

Here we assume this is created within an R package.

We define a user type.

type user: object {
  id: int,
  name: char
}

Now we can define a function that will create a user.

func create_user(): user {
  return user()
}

Now we can define our methods on the user object, we'll define two methods to update the id and the name of a user.

Set ID

Vapour

@generic
func (x: any) set_id(id: int, ...: any): any

#' @export
func (x: user) set_id(id: int, ...: any): user {
  stopifnot(!missing(id))
  x$id = id
  return x
}

R

set_id <- function(x, id, ...) {
  UseMethod("set_id")
}

set_id.user <- function(x, id, ...) {
  stopifnot(!missing(id))
  x$id <- id
  return(x)
}

Set name

Vapour

@generic
func (x: any) set_name(name: char, ...: any): any

#' @export
func (x: user) set_name(name: char, ...: any): user {
  stopifnot(!missing(name))
  x$name = name
  return x
}

R

set_name <- function(x, id, ...) {
  UseMethod("set_name")
}

set_name.user <- function(x, id, ...) {
  stopifnot(!missing(id))
  x$id <- id
  return(x)
}

With the methods created we can now used them!

Vapour

let john: user = create_user() |>
  set_id(1) |>
  set_name("John")

R

john = create_user() |>
  set_id(1) |>
  set_name("John")

Finally, you can transpile the code.

vapour -indir=vp