adding-to-ggplot2-object-with-other-stuff

library(ggplot2)

plot_diamonds <- function() {
  p <- ggplot(head(diamonds), aes(x = cut, y = price)) +
    geom_jitter()
  res <- list(
    name = "diamonds",
    p = p
  )
  class(res) <- "diamonds"
  res
}

print.diamonds <- function(x) {
  print(x[["p"]])
  invisible(x)
}

my_p <- plot_diamonds()

# Prints ggplot2 plot
my_p

# But $name is available too!
my_p$name
#> [1] "diamonds"

# If I try to add additional ggplot2 stuff...

# Doesn't work
my_p +
  ggtitle("Diamonds")
#> Error in my_p + ggtitle("Diamonds"): non-numeric argument to binary operator

# Works
my_p[["p"]] +
  ggtitle("Diamonds")

Is diamonds intended to be a subclass of ggplot?

You might need to redefine the + function so that for a diamonds object you call the + function on the ggplot part and keep the other stuff