10.10 Useful Examples - Wrapper

Useful when…

• You want to create a function that wraps a bunch of other functions

For example, ggsave() wraps a bunch of different graphics device functions:

# (Even more simplified)
plot_dev <- function(ext, dpi = 96) {
  force(dpi)
  
  switch(
    ext,
    svg = function(filename, ...) svglite::svglite(file = filename, ...),
    png = function(...) grDevices::png(..., res = dpi, units = "in"),
    jpg = ,
    jpeg = function(...) grDevices::jpeg(..., res = dpi, units = "in"),
    stop("Unknown graphics extension: ", ext, call. = FALSE)
  )
}

Then ggsave() uses

ggsave <- function(...) {
  dev <- plot_dev(device, filename, dpi = dpi)
  ...
  dev(filename = filename, width = dim[1], height = dim[2], bg = bg, ...)
  ...
}

Otherwise, would have to do something like like a bunch of if/else statements.