Produce boilerplate constructors — make

The make_constructor() functions sets up a user-facing constructor for ggproto classes. Currently, make_constructor() is implemented for Geom classes.

Usage

make_constructor(x, ...)

# S3 method for class 'Geom'
make_constructor(
  x,
  ...,
  checks = exprs(),
  omit = character(),
  env = caller_env()
)

# S3 method for class 'Stat'
make_constructor(
  x,
  ...,
  checks = exprs(),
  omit = character(),
  env = caller_env()
)

Arguments

x: An object to setup a constructor for.
...: Name-value pairs to use as additional arguments in the constructor. For layers, these are passed on to layer(params).
checks: A list of calls to be evaluated before construction of the object, such as one constructed with exprs().
omit: A character vector of automatically retrieved argument names that should not be converted to user-facing arguments. Useful for internally computed variables.
env: An environment to search for the object.

Value

A function

Examples

# For testing purposes, a geom that returns grobs
GeomTest <- ggproto(
  "GeomTest", Geom,
  draw_group = function(..., grob = grid::pointsGrob()) {
    return(grob)
  }
)
# Creating a constructor
geom_test <- make_constructor(GeomTest)

# Note that `grob` is automatically an argument to the function
names(formals(geom_test))
#> [1] "mapping"     "data"        "stat"        "position"   
#> [5] "..."         "grob"        "na.rm"       "show.legend"
#> [9] "inherit.aes"

# Use in a plot
set.seed(1234)
p <- ggplot(mtcars, aes(disp, mpg))
p + geom_test()

p + geom_test(grob = grid::circleGrob())


# The `checks` argument can be used to evaluate arbitrary expressions in
# the constructor before building the layer.
geom_path2 <- make_constructor(
  GeomPath, checks = rlang::exprs(
    match.arg(lineend, c("butt", "round", "square")),
    match.arg(linejoin, c("round", "mitre", "bevel"))
  )
)

# Note the inclusion of the expressions
print(geom_path2)
#> function (mapping = NULL, data = NULL, stat = "identity", position = "identity", 
#>     ..., arrow = NULL, arrow.fill = NULL, lineend = "butt", linejoin = "round", 
#>     linemitre = 10, na.rm = FALSE, show.legend = NA, inherit.aes = TRUE) 
#> {
#>     match.arg(lineend, c("butt", "round", "square"))
#>     match.arg(linejoin, c("round", "mitre", "bevel"))
#>     layer(mapping = mapping, data = data, geom = "path", stat = stat, 
#>         position = position, show.legend = show.legend, inherit.aes = inherit.aes, 
#>         params = list2(na.rm = na.rm, arrow = arrow, arrow.fill = arrow.fill, 
#>             lineend = lineend, linejoin = linejoin, linemitre = linemitre, 
#>             ...))
#> }
#> <environment: 0x562f6c271788>

# Argument mismatch is detected
try(geom_path2(linejoin = "foo"))
#> Error in match.arg(linejoin, c("round", "mitre", "bevel")) : 
#>   'arg' should be one of “round”, “mitre”, “bevel”