R devel - Aug 1997 - R-alpha: R-0.50-a3(+) Method despatching bug ?

It is very wierd...  Can some of you confirm the following behavior ?
It is a new bug (feature ?)  which was not yet in 0.49 ...




noquote <- function(obj) {
	## constructor for a useful "minor" class
	if(!inherits(obj,"noquote")) class(obj) <-
c(class(obj),"noquote")
	obj
}
"[.noquote" <- function (x, subs) structure(unclass(x)[subs], class
= "noquote")

print.noquote <- function(obj,...) {
	## method for (character) objects of class 'noquote'
	cl <- class(obj)
	class(obj) <- cl[cl != "noquote"]
	NextMethod("print", obj, quote = FALSE, ...)
}

nq <- noquote(letters)

##-- the next two should be equivalent, but are not ...?..
print(nq)
nq
> print(nq)
 [1] a b c d e f g h i j k l m n o p q r s t u v w x y z
> nq
Error: couldn't find function
"print.noquote"
> unclass(nq)
 [1] "a" "b" "c" "d" "e"
"f" "g" "h" "i" "j"
"k" "l" "m" "n" "o"
"p" "q" "r" "s"
[20] "t" "u" "v" "w" "x"
"y" "z"
> nq
Error: couldn't find function
"print.noquote"
> ls()
[1] "[.noquote"     "noquote"       "nq"          
"print.noquote"
> print.noquote
function (obj, ...) 
{
        ## method for (character) objects of class 'noquote'
        cl <- class(obj)
        class(obj) <- cl[cl != "noquote"]
        NextMethod("print", obj, quote = FALSE, ...)
}
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On Wed, 20 Aug 1997, Martin Maechler wrote:
> It is very wierd...  Can some of you confirm the following behavior ?
> It is a new bug (feature ?)  which was not yet in 0.49 ...
>
I'm not sure that you can expect NextMethod to work if you fiddle with the
class list...

However, there is still something wrong with method dispatching, since
print.noquote <- function (obj, ...)  NextMethod(quote = FALSE,...)
doesn't work either.  The error occurs when R tries for some reason to
make a recursive call to print.noquote.

Using debug() also shows the interesting fact that
R> nq 
calls print() with its arguments evaluated
------
debugging in: print(structure(c("a", "b", "c",
"d", "e", "f", "g", "h",
"i", 
"j", "k", "l", "m", "n",
"o", "p", "q", "r", "s",
"t", "u", "v",
"w", "x", "y", "z"), class =
"noquote"))
debugging in: print.noquote(structure(c("a", "b",
"c", "d", "e", "f", "g",
"h", "i", "j", "k", "l",
"m", "n", "o", "p", "q",
"r", "s", "t",
"u", "v", "w", "x", "y",
"z"), class = "noquote"))
Error: couldn't find function "print.noquote"
-------
but
----------
R> print(nq)
 print(nq)
debugging in: print(nq)
debugging in: print.noquote(nq)
 [1] a b c d e f g h i j k l m n o p q r s t u v w x y z
attr(,"class")
[1] noquote
exiting from: print.noquote(nq)
exiting from: print(nq)
----------
doesn't evaluate the argument first.




Thomas Lumley
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