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Conditionally Call a Function

Source: R/callIf.R
callIf.Rd

Conditionally evaluate a function depending on the value of an argument. This is a convenient helper for optional features such as plotting, logging, or callbacks, where the user can enable, disable, or parameterize a function call via a single argument.

Usage

callIf(fun, arg, defaults = NULL, forbidden = NULL, warn = TRUE)

Arguments

fun

a function to be called.

arg

controls whether and how fun is called:

  • FALSE, NULL, or NA: fun is not called and NULL is returned invisibly.

  • TRUE: fun is called with defaults (if provided), or with no arguments.

  • a fully named list: fun is called with the list elements as arguments. If defaults is provided, it is merged with arg, where elements of arg override those in defaults.

defaults

a named list of default arguments passed to fun when arg = TRUE, or used as a base when arg is a list. Default is NULL.

forbidden

optional character vector of argument names that are not allowed. If any of these appear in arg, they are removed before calling fun. A warning is issued unless warn = FALSE.

warn

logical. If TRUE (default), a warning is issued when forbidden arguments are removed.

Value

returns the result of fun(...) if called. If arg is FALSE, NULL, or NA, returns NULL invisibly.

Details

This function implements a flexible pattern for optional function calls:

  • Enable/disable behavior with TRUE/FALSE

  • Customize behavior with a list of arguments

  • Provide safe defaults and restrict certain arguments

When merging defaults and arg, user-supplied arguments take precedence. Unlike modifyList(), elements with the value NULL are preserved and passed on to fun (so that an explicit NULL can be used to reset an argument).

See also

Other pkg.args: extractArgs(), getDotsArg(), mergeArgs(), recycle()

Examples

# Simple usage: skip
callIf(message, FALSE)

# Call with defaults
callIf(message, TRUE, defaults = list("Hello world"))
#> Hello world

# Call with explicit arguments
callIf(message, list(x = "Hello from callIf"))
#> Hello from callIf

# With defaults + override
callIf(plot, list(x = 1:5),
       defaults = list(y = 1:5, type = "l"))


# Forbid arguments
callIf(plot,
       list(x = 1:5, y = 1:5, col = "red"),
       forbidden = "col")
#> Warning: Ignoring forbidden argument(s) for 'plot': col


# Typical use case: optional plotting
x <- 1:10
y <- x^2
callIf(plot, TRUE, defaults = list(x, y))