Currently, if one wants to test if an argument to an outer function is
missing from within an inner function, this works:
> g5 <- function(a) {
+ inner <- function(a) {
+ if (missing(a))
+ "outer arg is missing"
+ else
+ "found outer arg!"
+ }
+ inner(a)
+ }
> g5(3)
[1] "found outer arg!"
> g5()
[1] "outer arg is missing"
While if inner is defined as function() (without arguments) one gets
an error: 'missing' can only be used for arguments.
However, ?missing contains a note that this behavior is subject to
change.
I'm particularly interested in whether the code shown above will
continue to work. While it does what I want in this case, the
behavior seems a bit surprising since textually the call to inner does
provide an argument. So it seems possible that might change.
Can anyone provide more insight into how things may change?
Thanks.
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