不管参数是否有圆括号,都能使函数工作

我正在围绕某个包中的函数编写一个包装函数。该函数基本上为 ggplot 物体。但是,按照函数的实现方式,需要将主题参数指定为函数。但是我希望我的包装器函数能够工作,而不管参数是指定为函数还是主题对象。我该怎么做?

下面是函数的一个玩具示例,它工作的条件和不工作的条件:

# loading needed libraries
library(ggplot2)

# creating basic plot on which themes are to be added
plot <- ggplot(mtcars, aes(wt, mpg)) + geom_point()

# first attempt at the function
theme_adder1 <- function(ggplot.obj, ggtheme = ggplot2::theme_bw) {
  # this can't be modified (because it was written by someone else)
  ggplot.obj + ggtheme() 
}

# this works
theme_adder1(ggplot.obj = plot, ggtheme = ggplot2::theme_grey)

# this doesn't work
theme_adder1(ggplot.obj = plot, ggtheme = ggplot2::theme_grey())
#> Error in ggtheme(): could not find function "ggtheme"

# checking classes
class(ggplot2::theme_bw())
#> [1] "theme" "gg"
class(ggplot2::theme_bw)
#> [1] "function"

ggtheme theme function 对象,然后使用。但我不知道怎么做。

# second attempt at modifying function in a way that it will work irrespective
# of how the ggtheme argument is entered
theme_adder2 <- function(ggplot.obj, ggtheme = ggplot2::theme_bw) {
  if (class(ggtheme)[[1]] == "function") {
    ggplot.obj + ggtheme()
  } else if (class(ggtheme)[[1]] == "theme") {
    # what modifcation can be made here?
    ggtheme <- ??? 
    ggplot.obj + ggtheme()
  }
}

创建日期:2018-08-28 reprex package (v0.2.0.9000)。