Infinite recursion in as.data.table()

[beckerbenj]

Using as.data.table.data.frame() on a data.frame which inherits from another class leads to an infinite recursion. This seems to have been introduced in #6865 and also came up in #6874. The issue is caused in line 218 in as.data.table.R:

if (!identical(class(x), "data.frame")) return(as.data.table(as.data.frame(x), keep.rownames=keep.rownames, key=key, ...))

# Minimal reproducible example (not executed as this breaks reprex)

df1 <- data.frame(var1 = 1:10)
class(df1) <- c("data.frame", "someClass")
out <- data.table::as.data.table(df1)

[MichaelChirico]

as noted in #6874 I think this is the fault of a bug in your as.data.frame method. anyway this is a duplicate.

[beckerbenj]

This was indirectly filed to me as a bug report by someone who uses one of my packages (which uses as.data.table()). I agree that this is their fault, but it still can be quite cumbersome to debug for packages using data.table especially as this simply leads to a C stack error.