match.fun

R Base 3.6.2

When called inside functions that take a function as argument, extract the desired function object while avoiding undesired matching to objects of other types.

Syntax

match.fun(FUN, descend = TRUE)

Arguments

Parameter	Description
`FUN`	item to match as function: a function, symbol or character string. See ‘Details’.
`descend`	logical; control whether to search past non-function objects.

Return Value

A function matching FUN or an error is generated.

Details

match.fun is not intended to be used at the top level since it will perform matching in the parent of the caller. If FUN is a function, it is returned. If it is a symbol (for example, enclosed in backquotes) or a character vector of length one, it will be looked up using get in the environment of the parent of the caller. If it is of any other mode, it is attempted first to get the argument to the caller as a symbol (using substitute twice), and if that fails, an error is declared. If descend = TRUE, match.fun will look past non-function objects with the given name; otherwise if FUN points to a non-function object then an error is generated. This is used in base functions such as apply, lapply, outer, and sweep.

Examples

Example

# NOT RUN {
# Same as get("*"):
match.fun("*")
# Overwrite outer with a vector
outer <- 1:5
try(match.fun(outer, descend = FALSE)) #-> Error:  not a function
match.fun(outer) # finds it anyway
is.function(match.fun("outer")) # as well
# }