S4 class [ (subset) inheritance with additional arguments

Question

This is an extension of Using callNextMethod() within accessor function in R.

Update 2017-03-25: To illustrate how this only fails when loading the methods, but not when it's in a built package, I created a dummy package: https://github.com/zkamvar/inheritest#readme

Basic problem:

I have a class bar that inherits another class foo, and both of them have additional arguments for the [ method. The method for foo works consistently, but the method for bar fails after the first use.

Error and Traceback:

Error in callNextMethod(x, i, j, ..., drop): bad object found as method (class "function")

4: stop(gettextf("bad object found as method (class %s)",  dQuote(class(method))), 
   domain = NA)
3: callNextMethod(x, i, j, ..., drop) at #9
2: .local(x, i, j, ..., drop = drop)
1: BAR["x"]

Further details:

I have a package that implements a class that depends on a class from another package. When the packages are built, everything works fine, but when my package is simply loaded (using devtools::load_all(".")), I get the behavior below.

Minimum Working Example:

foo <- setClass("foo", representation(x = "numeric", y = "numeric"))
bar <- setClass("bar", representation(distance = "numeric"), contains = "foo")

setMethod(f = "[", signature = signature(x = "foo", i = "ANY", j = "ANY", drop = "ANY"), 
  definition = function(x, i, j, ..., foo = TRUE, drop = FALSE) {
    if (foo) 
      message("FOOOOOOO")
    if (i == "x") {
      return(x@x)
    } else {
      if (i == "y") {
        return(x@y)
      }
    }
  })
#> [1] "["

setMethod(f = "[", signature = signature(x = "bar", i = "ANY", j = "ANY", drop = "ANY"), 
  definition = function(x, i, j, ..., bar = TRUE, drop = FALSE) {
    if (bar) 
      message("BAAAAAAR")
    if (i == "distance") {
      return(x@distance)
    } else {
      callNextMethod(x, i, j, ..., drop)
    }
  })
#> [1] "["

FOO <- new("foo", x = 1, y = 4)
BAR <- new("bar", x = 1, y = 4, distance = 3)
FOO["x"]
#> FOOOOOOO
#> [1] 1
BAR["x"]
#> BAAAAAAR
#> FOOOOOOO
#> [1] 1
FOO["x"]
#> FOOOOOOO
#> [1] 1
BAR["distance"]
#> BAAAAAAR
#> [1] 3
BAR["x"]  # fails
#> BAAAAAAR
#> Error in callNextMethod(x, i, j, ..., drop): bad object found as method (class "function")
BAR["x", foo = FALSE]
#> BAAAAAAR
#> [1] 1

Note: when I passed this through reprex, The first and last calls to BAR resulted in errors as well, but I am showing what I experience in an interactive session. I am using R version 3.3.3

Answer 1

This is because callNextMethod() is not smart enough to handle methods on primitives with augmented formals. I've fixed it and will commit to trunk soon.