Thanks. That's helpful. It also works in my use case with R6 classes,
even if I don't include the "R6Class" in the setOldClass definition.
--Russell
On 12/12/25 08:49, Mikael Jagan wrote:
> S4 is "formal", so you need to declare inheritance:
>
> setOldClass(c("SubClass", "SuperClass"))
>
> This usage (first argument of length greater than one) is documented by
> help("setOldClass") including among the examples where analogously I see
>
> setOldClass(c("mlm", "lm"))
>
> and there are more examples in the list of old classes defined by
> 'methods',
> exported as '.OldClassesList'.
>
> Mikael
>
>
>> Date: Thu, 11 Dec 2025 17:10:28 -0500
>> From: Russell Almond<[email protected]>
>>
>> I noticed this problem while working with R6 objects, but I can
>> reproduce it using S3 classes.
>>
>> If I define a method on the S3 superclass, the subclass doesn't
>> inherit it.
>>
>> ``` r
>> library(methods)
>>
>> SuperClass <- function(n) {
>> result <- list(n=n)
>> class(result) <- "SuperClass"
>> result
>> }
>>
>> setOldClass("SuperClass")
>>
>> setGeneric("sampleSize",function(x) {standardGeneric("sampleSize")})
>> #> [1] "sampleSize"
>>
>> setMethod("sampleSize","SuperClass", function(x) {x$n})
>>
>> SubClass <- function (n) {
>> result <- SuperClass(n)
>> class(result) <- c("SubClass",class(result))
>> result
>> }
>>
>> setOldClass("SubClass")
>>
>> example <- SubClass(7)
>> class(example)
>> #> [1] "SubClass" "SuperClass"
>> is(example,"SuperClass")
>> #> [1] TRUE
>> methods("sampleSize")
>> #> [1] sampleSize,SuperClass-method
>> #> see '?methods' for accessing help and source code
>> sampleSize(example)
>> #> Error: unable to find an inherited method for function 'sampleSize'
>> for signature 'x = "SubClass"'
>> ```
>>
>> <sup>Created on 2025-12-11 with [reprex
>> v2.1.1](https://reprex.tidyverse.org)</sup>
>>
>> I'm using R 4.5.2 and the same version of methods.
>>
>> Is this a bug?
>>
>> --Russell
>>
>>
>> -- Russell Almond https://ralmond.net/ [[alternative HTML version
>> deleted]]
>
--
Russell Almond
https://ralmond.net/
[[alternative HTML version deleted]]
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