"Incompatible methods" for overloaded operator

I'm trying to overload an operator, and I'm running into a strange problem.
It happens when I install and load the package, but not when I simply
source() the code.

I'm defining + for two classes. The R code looks like this:
#' @export
#' @method "+" a
`+.a` <- function (x1, x2) {
? ?message("Running custom + function")
}

#' @export
#' @method "+" b
`+.b` <- `+.a`

In some cases I do a+b, and in other cases, I do b+b. I'm told that the +.a
and +.b functions must be identical to avoid the error about "Incompatible
methods". (In the actual code, the overloaded + function checks the classes
of x1 and x2, and then sends them off to other functions.)

This is the NAMESPACE file:
S3method("+",a)
S3method("+",b)

I've put the code up at https://github.com/wch/badadd.



If I just cut and paste the function definitions to my R session, it works
fine:
x + y
# Running + function
# NULL


However, if I install and load the package, it gives a warning about
incompatible methods, and then seems to fall back to the arithmetic +
operator:
library(badadd)
x + y
# [1] 3
# attr(,"class")
# [1] "a"
# Warning message:
# Incompatible methods ("+.a", "+.b") for "+"


Is this expected behavior? And if so, is there a workaround?
-Winston

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Hi all,

Any ideas about this?  As far as I can tell it should work - and I
don't understand why it's ok when run outside of a package.

Hadley

On Wed, Jun 13, 2012 at 7:41 PM, Winston Chang<winstonchang1 at gmail.com>  wrote:

I'm trying to overload an operator, and I'm running into a strange problem.
It happens when I install and load the package, but not when I simply
source() the code.

I'm defining + for two classes. The R code looks like this:
#' @export
#' @method "+" a
`+.a`<- function (x1, x2) {
    message("Running custom + function")
}

#' @export
#' @method "+" b
`+.b`<- `+.a`

In some cases I do a+b, and in other cases, I do b+b. I'm told that the +.a
and +.b functions must be identical to avoid the error about "Incompatible
methods". (In the actual code, the overloaded + function checks the classes
of x1 and x2, and then sends them off to other functions.)

This is the NAMESPACE file:
S3method("+",a)
S3method("+",b)

I've put the code up at https://github.com/wch/badadd.



If I just cut and paste the function definitions to my R session, it works
fine:
x + y
# Running + function
# NULL


However, if I install and load the package, it gives a warning about
incompatible methods, and then seems to fall back to the arithmetic +
operator:
library(badadd)
x + y
# [1] 3
# attr(,"class")
# [1] "a"
# Warning message:
# Incompatible methods ("+.a", "+.b") for "+"


Is this expected behavior? And if so, is there a workaround?
-Winston

        [[alternative HTML version deleted]]

from ?groupGeneric under 'Ops' (of which "+" is one)

? ? ? ? ?used. ?If different methods are found, there is a warning
? ? ? ? ?about 'incompatible methods': in that case or if no method is
? ? ? ? ?found for either argument the internal method is used.

which doesn't really explain why it works at the command line but not in a
package. S4 methods can be defined on both arguments, so

?setClass("A", contains="numeric")
?setClass("B", contains="numeric")

?setMethod("+", c("A", "A"), function(e1, e2) message("A + A"))
?setMethod("+", c("A", "B"), function(e1, e2) message("A + B"))
?setMethod("+", c("B", "A"), function(e1, e2) message("B + A"))
?setMethod("+", c("B", "B"), function(e1, e2) message("B + B"))

with

?exportClasses("A", "B")
?exportMethods("+")

and then

new("A") + new("B")

A + B
NULL

from ?groupGeneric under 'Ops' (of which "+" is one)

          used.  If different methods are found, there is a warning
          about 'incompatible methods': in that case or if no method is
          found for either argument the internal method is used.

which doesn't really explain why it works at the command line but not in a
package. S4 methods can be defined on both arguments, so

But aren't the methods compatible?  If equality doesn't make a method
compatible what does?

  setClass("A", contains="numeric")
  setClass("B", contains="numeric")

  setMethod("+", c("A", "A"), function(e1, e2) message("A + A"))
  setMethod("+", c("A", "B"), function(e1, e2) message("A + B"))
  setMethod("+", c("B", "A"), function(e1, e2) message("B + A"))
  setMethod("+", c("B", "B"), function(e1, e2) message("B + B"))

with

  exportClasses("A", "B")
  exportMethods("+")

and then

new("A") + new("B")

A + B
NULL

But unfortunately that doesn't work for S3 classes (even with
setOldClass) so it doesn't help much unless we want to rewrite
everything in S4 :/

Hadley

On Wed, Jun 20, 2012 at 10:49 PM, Martin Morgan <mtmorgan at fhcrc.org> wrote:

On 06/20/2012 08:06 PM, Hadley Wickham wrote:

But aren't the methods compatible? ?If equality doesn't make a method
compatible what does?

Actually I guess that turns out to be the key (to why they work at the
command line but not in a package). ?At the command line they really _are_
the same, e.g., .Internal(inspect("+.a")) has the same ?address as "+.b".
In the package they (e.g., badadd:::"+.a") have different addresses, I
suppose because S3method() acts on them independently.

Thanks for the investigation. I wonder if there's some sort of workaround.

But unfortunately that doesn't work for S3 classes (even with
setOldClass) so it doesn't help much unless we want to rewrite
everything in S4 :/

rewrite?

Yes, the original question is the result of some issues that came up in
ggplot2 development...

-Winston

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