Improving user-friendliness of S4 dispatch failure when mis-naming arguments?
Here's a trivial patch that offers some improvement:
Index: src/library/methods/R/methodsTable.R
===================================================================
--- src/library/methods/R/methodsTable.R (revision 84931)
+++ src/library/methods/R/methodsTable.R (working copy)
@@ -752,11 +752,12 @@
if(length(methods) == 1L)
return(methods[[1L]]) # the method
else if(length(methods) == 0L) {
- cnames <- paste0("\"", vapply(classes, as.character, ""), "\"",
+ cnames <- paste0(head(fdef at signature, length(classes)), "=\"",
vapply(classes, as.character, ""), "\"",
collapse = ", ")
stop(gettextf("unable to find an inherited method for function %s
for signature %s",
sQuote(fdef at generic),
sQuote(cnames)),
+ call. = FALSE,
domain = NA)
}
else
Here's the upshot for the example on DBI:
dbGetQuery(connection = conn, query = query)
Error: unable to find an inherited method for function ?dbGetQuery?
for signature ?conn="missing", statement="missing"?
I don't have any confidence about edge cases / robustness of this
patch for generic S4 use cases (make check-all seems fine), but I
don't suppose a full patch would be dramatically different from the
above.
Mike C
On Thu, Aug 10, 2023 at 12:39?PM Gabriel Becker <gabembecker at gmail.com> wrote:
I just want to add my 2 cents that I think it would be very useful and beneficial to improve S4 to surface that information as well. More information about the way that the dispatch failed would be of great help in situations like the one Michael pointed out. ~G On Thu, Aug 10, 2023 at 9:59?AM Michael Chirico via R-devel <r-devel at r-project.org> wrote:
I forwarded that along to the original reporter with positive feedback -- including the argument names is definitely a big help for cuing what exactly is missing. Would a patch to do something similar for S4 be useful? On Thu, Aug 10, 2023 at 6:46?AM Hadley Wickham <h.wickham at gmail.com> wrote:
Hi Michael,
I can't help with S4, but I can help to make sure this isn't a problem
with S7. What do you think of the current error message? Do you see
anything obvious we could do to improve?
library(S7)
dbGetQuery <- new_generic("dbGetQuery", c("conn", "statement"))
dbGetQuery(connection = NULL, query = NULL)
#> Error: Can't find method for generic `dbGetQuery(conn, statement)`:
#> - conn : MISSING
#> - statement: MISSING
Hadley
On Wed, Aug 9, 2023 at 10:02?PM Michael Chirico via R-devel
<r-devel at r-project.org> wrote:
I fielded a debugging request from a non-expert user today. At root was running the following: dbGetQuery(connection = conn, query = query) The problem is that they've named the arguments incorrectly -- it should have been [1]: dbGetQuery(conn = conn, statement = query) The problem is that the error message "looks" highly confusing to the untrained eye: Error in (function (classes, fdef, mtable) : unable to find an inherited method for function ?dbGetQuery? for signature ?"missing", "missing"? In retrospect, of course, this makes sense -- the mis-named arguments are getting picked up by '...', leaving the required arguments missing. But I was left wondering how we could help users right their own ship here. Would it help to mention the argument names? To include some code checking for weird combinations of missing arguments? Any other suggestions? Mike C [1] https://github.com/r-dbi/DBI/blob/97934c885749dd87a6beb10e8ccb6a5ebea3675e/R/dbGetQuery.R#L62-L64
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