Question

Since length is a generic method, why can’t I do

length.character <- nchar

? It seems that strings are treated special in R. Is there a reason for that? Would you discourage defining functions like head.character and tail.character?

Answer 1

If you look at the help page for InternalMethods (mentioned in the details portion of the help page for length) it states that

For efficiency, internal dispatch only
occurs on objects, that
is those for which ‘is.object’ returns true.

Vectors are not objects in the same sense as other objects are, so the method dispatch is not being done on any basic vectors (not just character). if you really want to use this type of dispatch you need a defined object, e.g.:

> tmp <- state.name
> class(tmp) <- 'mynewclass'
> length.mynewclass <- nchar
> length(tmp)
 [1]  7  6  7  8 10  8 11  8  7  7  6  5  8  7  4  6  8  9  5  8 13  8  9 11  8
[26]  7  8  6 13 10 10  8 14 12  4  8  6 12 12 14 12  9  5  4  7  8 10 13  9  7
>