cli_format_method {cli}

Create a format method for an object using cli tools

Description

This method can be typically used in format() S3 methods. Then the print() method of the class can be easily defined in terms of such a format() method. See examples below.

Usage

cli_format_method(expr, theme = getOption("cli.theme"))

Arguments

expr

Expression that calls ⁠cli_*⁠ methods, base::cat() or base::print() to format an object's printout.

theme

Theme to use for the formatting.

Value

Character vector, one element for each line of the printout.

Examples

# Let's create format and print methods for a new S3 class that
# represents the an installed R package: `r_package`

# An `r_package` will contain the DESCRIPTION metadata of the package
# and also its installation path.
new_r_package <- function(pkg) {
  tryCatch(
    desc <- packageDescription(pkg),
    warning = function(e) stop("Cannot find R package `", pkg, "`")
  )
  file <- dirname(attr(desc, "file"))
  if (basename(file) != pkg) file <- dirname(file)
  structure(
    list(desc = unclass(desc), lib = dirname(file)),
    class = "r_package"
  )
}

format.r_package <- function(x, ...) {
  cli_format_method({
    cli_h1("{.pkg {x$desc$Package}} {cli::symbol$line} {x$desc$Title}")
    cli_text("{x$desc$Description}")
    cli_ul(c(
      "Version: {x$desc$Version}",
      if (!is.null(x$desc$Maintainer)) "Maintainer: {x$desc$Maintainer}",
      "License: {x$desc$License}"
    ))
    if (!is.na(x$desc$URL)) cli_text("See more at {.url {x$desc$URL}}")
  })
}

# Now the print method is easy:
print.r_package <- function(x, ...) {
  cat(format(x, ...), sep = "\n")
}

# Try it out
new_r_package("cli")

# The formatting of the output depends on the current theme:
opt <- options(cli.theme = simple_theme())
print(new_r_package("cli"))
options(opt)  # <- restore theme