R/DistributionDecorator.R

In distr6: The Complete R6 Probability Distributions Interface

#' @name DistributionDecorator
#'
#' @title Abstract DistributionDecorator Class
#'
#' @template class_abstract
#' @template field_packages
#' @template method_initialize
#' @template method_decorate
#'
#' @details Decorating is the process of adding methods to classes that are not part of the core
#' interface (Gamma et al. 1994). Use [listDecorators] to see which decorators are currently
#' available. The primary use-cases are to add numeric results when analytic ones are missing,
#' to add complex modelling functions and to impute missing d/p/q/r functions.
#'
#' Use [decorate] or `$decorate` to decorate distributions.
#'
#' @references
#' Gamma, Erich, Richard Helm, Ralph Johnson, and John Vlissides. 1994. “Design Patterns: Elements
#' of Reusable Object-Oriented Software.” Addison-Wesley.
#'
#' @export
DistributionDecorator <- R6Class("DistributionDecorator",
  public = list(
    packages = NULL,

    #' @description
    #' Creates a new instance of this [R6][R6::R6Class] class.
    initialize = function() {
      abstract(self, "DistributionDecorator", "listDecorators()")
    },

    #' @description
    #' Decorates the given distribution with the methods available in this decorator.
    #' @param ... `ANY` \cr
    #' Extra arguments passed down to specific decorators.
    decorate = function(distribution, ...) {

      assert_pkgload(self$packages)
      dec_name <- getR6Class(self)

      if (dec_name %in% distribution$decorators) {
        message(paste(
          distribution$name, "is already decorated with",
          paste0(dec_name, collapse = ",")
        ))
        invisible(self)

      } else {
        methods <- setdiff(self$methods, names(distribution))

        env <- as.environment(distribution)
        for (i in seq_along(methods)) {
          fun <- function() {}
          formals(fun) <- c(
            formals(self[[methods[[i]]]]),
            list(self = distribution),
            list(private = distribution$.__enclos_env__$private)
          )
          body(fun) <- body(self[[methods[[i]]]])
          assign(methods[[i]], fun, envir = env)
        }

        message(paste(distribution$name, "is now decorated with", dec_name))
        distribution$.__enclos_env__$private$.updateDecorators(c(distribution$decorators, dec_name))
        invisible(self)
      }
    }
  ),

  active = list(
    #' @field methods
    #' Returns the names of the available methods in this decorator.
    methods = function() {
      setdiff(
        names(self),
        c(".__enclos_env__", "methods", "packages", "clone", "decorate", "initialize")
      )
    }
  )
)