Message-ID: <57156F2B.4000205@ivt.baug.ethz.ch>
Date: 2016-04-18T23:35:07Z
From: Kirill Müller
Subject: S3 dispatch for S4 subclasses only works if variable "extends" is accessible from global environment
Scenario: An S3 method is declared for an S4 base class but called for
an instance of a derived class.
Steps to reproduce:
> Rscript -e "test <- function(x) UseMethod('test', x); test.Matrix <-
function(x) 'Hi'; MatrixDispatchTest::test(Matrix::Matrix())"
Error in UseMethod("test", x) :
no applicable method for 'test' applied to an object of class "lsyMatrix"
Calls: <Anonymous>
1: MatrixDispatchTest::test(Matrix::Matrix())
> Rscript -e "extends <- 42; test <- function(x) UseMethod('test', x);
test.Matrix <- function(x) 'Hi'; MatrixDispatchTest::test(Matrix::Matrix())"
[1] "Hi"
To me, it looks like a sanity check in line 655 of src/main/attrib.c is
making wrong assumptions, but there might be other reasons.
(https://github.com/wch/r-source/blob/780021752eb83a71e2198019acf069ba8741103b/src/main/attrib.c#L655-L656)
Same behavior in R 3.2.4, R 3.2.5 and R-devel r70420.
Best regards
Kirill