match.fun {base}R Documentation

Function Verification for ``Function Variables''

Description

This function is called inside functions that take a function as argument. It's purpose is to extract the desired function object while avoiding undesired matching to objects of other types.

Usage

match.fun(FUN, descend = TRUE)

Arguments

FUN item to match as function.
descend logical; control whether to search past non-function objects.

Details

match.fun is not intended to be used at the top level since it will perform matching in the parent of the caller.

It is assumed that FUN is an argument passed to the caller and is a function or a character string containing the name of a function.

Returns an error if no matching function is found.

Value

A function matching FUN or an error is generated.

Bugs

The descend argument is a bit of misnomer and probably not actually needed by anything. It may go away in the future.

It is impossible to fully foolproof this. If one attaches a list or data frame containing a character object with the same name of a system function, it will be used.

Author(s)

Peter Dalgaard and Robert Gentleman, based on an earlier version by Jonathan Rougier

See Also

match.arg, get

Examples

# Same as get("*"):
match.fun("*")
# Overwrite outer with a vector
outer <- 1:5

match.fun(outer, descend = FALSE) #-> Error:  not a function

match.fun(outer) # finds it anyway
is.function(match.fun("outer")) # as well


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