[Rd] Improving user-friendliness of S4 dispatch failure when mis-naming arguments?

[Michael Chirico]

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 using signature, length(classes)), "=\"",
vapply(classes, as.character, ""), "\"",
      collapse = ", ")
     stop(gettextf("unable to find an inherited method for function %s
for signature %s",
                   sQuote(fdef using 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 using 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 using 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 using 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 using 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
>> > >
>> > > ______________________________________________
>> > > R-devel using r-project.org mailing list
>> > > https://stat.ethz.ch/mailman/listinfo/r-devel
>> >
>> >
>> >
>> > --
>> > http://hadley.nz
>>
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