POC: double dispatch for ggplot_add()

DESCRIPTION

@@ -40,6 +40,7 @@ Imports:
     MASS,
     mgcv,
     rlang (>= 1.1.0),
+    S7,
     scales (>= 1.2.0),
     stats,
     tibble,
@@ -90,6 +91,7 @@ Collate:
     'compat-plyr.R'
     'utilities.R'
     'aes.R'
+    'all-classes.R'
     'utilities-checks.R'
     'legend-draw.R'
     'geom-.R'
@@ -196,9 +198,9 @@ Collate:
     'margins.R'
     'performance.R'
     'plot-build.R'
+    'plot.R'
     'plot-construction.R'
     'plot-last.R'
-    'plot.R'
     'position-.R'
     'position-collide.R'
     'position-dodge.R'

NAMESPACE

@@ -51,20 +51,6 @@ S3method(get_alt_text,ggplot_built)
 S3method(get_alt_text,gtable)
 S3method(ggplot,"function")
 S3method(ggplot,default)
-S3method(ggplot_add,"NULL")
-S3method(ggplot_add,"function")
-S3method(ggplot_add,Coord)
-S3method(ggplot_add,Facet)
-S3method(ggplot_add,Guides)
-S3method(ggplot_add,Layer)
-S3method(ggplot_add,Scale)
-S3method(ggplot_add,by)
-S3method(ggplot_add,data.frame)
-S3method(ggplot_add,default)
-S3method(ggplot_add,labels)
-S3method(ggplot_add,list)
-S3method(ggplot_add,theme)
-S3method(ggplot_add,uneval)
 S3method(ggplot_build,ggplot)
 S3method(ggplot_gtable,ggplot_built)
 S3method(grid.draw,absoluteGrob)
@@ -228,6 +214,7 @@ export(PositionJitter)
 export(PositionJitterdodge)
 export(PositionNudge)
 export(PositionStack)
+export(S7_ggplot)
 export(Scale)
 export(ScaleBinned)
 export(ScaleBinnedPosition)

R/all-classes.R

@@ -0,0 +1,11 @@
+# Class declarations for S7 dispatch.
+class_theme  <- S7::new_S3_class("theme")
+class_scale  <- S7::new_S3_class("Scale")
+class_labels <- S7::new_S3_class("labels")
+class_guides <- S7::new_S3_class("Guides")
+class_aes    <- S7::new_S3_class("uneval")
+class_coord  <- S7::new_S3_class("Coord")
+class_facet  <- S7::new_S3_class("Facet")
+class_by     <- S7::new_S3_class("by")
+class_layer  <- S7::new_S3_class("Layer")
+class_scales_list <- S7::new_S3_class("ScalesList")

R/plot-construction.R

@@ -1,3 +1,6 @@
+#' @include plot.R
+NULL
+
 #' Add components to a plot
 #'
 #' `+` is the key to constructing sophisticated ggplot2 graphics. It
@@ -70,7 +73,7 @@ add_ggplot <- function(p, object, objectname) {
   if (is.null(object)) return(p)
 
   p <- plot_clone(p)
-  p <- ggplot_add(object, p, objectname)
+  p <- ggplot_add(object, p, object_name = objectname)
   set_last_plot(p)
   p
 }
@@ -81,105 +84,124 @@ add_ggplot <- function(p, object, objectname) {
 #'
 #' @param object An object to add to the plot
 #' @param plot The ggplot object to add `object` to
-#' @param object_name The name of the object to add
+#' @param ... Additional arguments to pass to the methods. Typically, an
+#'   `object_name` argument that gives a display name for `object` to use
+#'   in error messages.
 #'
 #' @return A modified ggplot object
 #'
 #' @keywords internal
 #' @export
-ggplot_add <- function(object, plot, object_name) {
-  UseMethod("ggplot_add")
-}
-#' @export
-ggplot_add.default <- function(object, plot, object_name) {
-  cli::cli_abort("Can't add {.var {object_name}} to a {.cls ggplot} object.")
-}
-#' @export
-ggplot_add.NULL <- function(object, plot, object_name) {
-  plot
-}
-#' @export
-ggplot_add.data.frame <- function(object, plot, object_name) {
-  plot$data <- object
-  plot
-}
-#' @export
-ggplot_add.function <- function(object, plot, object_name) {
-  cli::cli_abort(c(
-          "Can't add {.var {object_name}} to a {.cls ggplot} object",
-    "i" = "Did you forget to add parentheses, as in {.fn {object_name}}?"
-  ))
-}
-#' @export
-ggplot_add.theme <- function(object, plot, object_name) {
-  plot$theme <- add_theme(plot$theme, object)
-  plot
-}
-#' @export
-ggplot_add.Scale <- function(object, plot, object_name) {
-  plot$scales$add(object)
-  plot
-}
-#' @export
-ggplot_add.labels <- function(object, plot, object_name) {
-  update_labels(plot, object)
-}
-#' @export
-ggplot_add.Guides <- function(object, plot, object_name) {
-  update_guides(plot, object)
-}
-#' @export
-ggplot_add.uneval <- function(object, plot, object_name) {
-  plot$mapping <- defaults(object, plot$mapping)
-  # defaults() doesn't copy class, so copy it.
-  class(plot$mapping) <- class(object)
-
-  labels <- make_labels(object)
-  names(labels) <- names(object)
-  update_labels(plot, labels)
-}
-#' @export
-ggplot_add.Coord <- function(object, plot, object_name) {
-  if (!isTRUE(plot$coordinates$default)) {
-    cli::cli_inform("Coordinate system already present. Adding new coordinate system, which will replace the existing one.")
+ggplot_add <- S7::new_generic("ggplot_add", c("object", "plot"))
+
+S7::method(ggplot_add, list(S7::class_any, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    cli::cli_abort("Can't add {.var {object_name}} to a {.cls ggplot} object.")
   }
 
-  plot$coordinates <- object
-  plot
-}
-#' @export
-ggplot_add.Facet <- function(object, plot, object_name) {
-  plot$facet <- object
-  plot
-}
-#' @export
-ggplot_add.list <- function(object, plot, object_name) {
-  for (o in object) {
-    plot <- plot %+% o
+# Cannot currently double dispatch on NULL directly
+# replace `S7::new_S3_class("NULL")` with `NULL` when S7 version > 0.1.1
+S7::method(ggplot_add, list(S7::new_S3_class("NULL"), S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot
   }
-  plot
-}
-#' @export
-ggplot_add.by <- function(object, plot, object_name) {
-  ggplot_add.list(object, plot, object_name)
-}
 
-#' @export
-ggplot_add.Layer <- function(object, plot, object_name) {
-  plot$layers <- append(plot$layers, object)
-
-  # Add any new labels
-  mapping <- make_labels(object$mapping)
-  default <- lapply(make_labels(object$stat$default_aes), function(l) {
-    attr(l, "fallback") <- TRUE
-    l
-  })
-  new_labels <- defaults(mapping, default)
-  current_labels <- plot$labels
-  current_fallbacks <- vapply(current_labels, function(l) isTRUE(attr(l, "fallback")), logical(1))
-  plot$labels <- defaults(current_labels[!current_fallbacks], new_labels)
-  if (any(current_fallbacks)) {
-    plot$labels <- defaults(plot$labels, current_labels)
-  }
-  plot
-}
+S7::method(ggplot_add, list(S7::class_data.frame, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot$data <- object
+    plot
+  }
+
+S7::method(ggplot_add, list(S7::class_function, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    cli::cli_abort(c(
+      "Can't add {.var {object_name}} to a {.cls ggplot} object",
+      "i" = "Did you forget to add parentheses, as in {.fn {object_name}}?"
+    ))
+  }
+
+S7::method(ggplot_add, list(class_theme, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot$theme <- add_theme(plot$theme, object)
+    plot
+  }
+
+S7::method(ggplot_add, list(class_scale, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot$scales$add(object)
+    plot
+  }
+
+S7::method(ggplot_add, list(class_labels, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    update_labels(plot, object)
+  }
+
+S7::method(ggplot_add, list(class_guides, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    update_guides(plot, object)
+  }
+
+S7::method(ggplot_add, list(class_aes, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    mapping <- defaults(object, plot$mapping)
+    # defaults() doesn't copy class, so copy it.
+    class(mapping) <- class(object)
+    S7::prop(plot, "mapping") <- mapping
+
+
+    labels <- make_labels(object)
+    names(labels) <- names(object)
+    update_labels(plot, labels)
+  }
+
+S7::method(ggplot_add, list(class_coord, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    if (!isTRUE(plot$coordinates$default)) {
+      cli::cli_inform("Coordinate system already present. Adding new coordinate system, which will replace the existing one.")
+    }
+
+    plot$coordinates <- object
+    plot
+  }
+
+S7::method(ggplot_add, list(class_facet, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot$facet <- object
+    plot
+  }
+
+S7::method(ggplot_add, list(S7::class_list, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    for (o in object) {
+      plot <- plot %+% o
+    }
+    plot
+  }
+
+S7::method(ggplot_add, list(class_by, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    S7::method(ggplot_add, list(class_list, ggplot))(
+      object, plot, object_name
+    )
+  }
+
+S7::method(ggplot_add, list(class_layer, S7_ggplot)) <-
+  function(object, plot, object_name) {
+    plot$layers <- append(plot$layers, object)
+
+    # Add any new labels
+    mapping <- make_labels(object$mapping)
+    default <- lapply(make_labels(object$stat$default_aes), function(l) {
+      attr(l, "fallback") <- TRUE
+      l
+    })
+    new_labels <- defaults(mapping, default)
+    current_labels <- plot$labels
+    current_fallbacks <- vapply(current_labels, function(l) isTRUE(attr(l, "fallback")), logical(1))
+    plot$labels <- defaults(current_labels[!current_fallbacks], new_labels)
+    if (any(current_fallbacks)) {
+      plot$labels <- defaults(plot$labels, current_labels)
+    }
+    plot
+  }