[Rd] R 2.5.0 devel try issue in conjuntion with S4 method dispatch

Seth Falcon sfalcon at fhcrc.org
Thu Mar 15 23:05:32 CET 2007

ml-it-r-devel at epigenomics.com writes:
> Investigating this new implementation I come across an issue in
> conjuntion with using S4 classes and methods. try(expr) does not return an
> object with attribute 'try-error' in case of method dispatch failure
> in the wrapped expression which to me seems not
> quite correct.

We've seen some similar issues but had not had time to track them

> Examples to reproduce the observation:

It isn't S4 specific.  The issue seems more about anonymous

   ll = list()
   ll[[1]] = function(x) stop("died")
   v = try(do.call(ll[[1]], list(1)), silent=TRUE)
   Error in as.list(call)[[1]] == "doTryCatch" : 
   	comparison (1) is possible only for atomic and list types
   > v
   Error: object "v" not found

I don't fully understand why the call is being computed, but the
following seems to get things going.

+ seth

--- a/src/library/base/R/New-Internal.R
+++ b/src/library/base/R/New-Internal.R
@@ -7,7 +7,8 @@ try <- function(expr, silent = FALSE) {
             ## Patch up the call to produce nicer result for testing as
             ## try(stop(...)).  This will need adjusting if the
             ## implementation of tryCatch changes.
-            if (as.list(call)[[1]] == "doTryCatch")
+            callFun <- as.list(call)[[1]]
+            if (is.name(callFun) && callFun == "doTryCatch")
                 call <- sys.call(-4)
             dcall <- deparse(call)[1]
             prefix <- paste("Error in", dcall, ": ")

Seth Falcon | Computational Biology | Fred Hutchinson Cancer Research Center

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